Measurement of jejunal surface pH in situ by plastic pH electrode in patients with coeliac disease

Attaching plastic pH electrodes to a Crosby capsule provides a means of measuring mucosal surface pH in the small intestine during jejunal biopsy. Plastic electrodes, with operating characteristics comparable to glass electrodes within the physiological pH range, were selected because of their mechanical flexibility. The sensing tip can be placed close to the capsule aperture to facilitate contact with the intestinal mucosa. Using this system, the jejunal mucosal surface pH was found to be 5.97 +/- 0.07 in 15 control subjects. In contrast, 13 coeliac patients had a significantly (p less than 0.001) higher jejunal surface pH of 6.73 +/- 0.15, subdivisible into 4 untreated patients with a mean value of 6.95 +/- 0.33 and 9 patients on a gluten-free diet with a mean value of 6.63 +/- 0.15, both higher (p less than 0.01, p less than 0.005) than the control value. An elevated jejunal surface pH in coeliac disease was associated with partial or subtotal villous atrophy and with low brush border enzyme activities. Confirming previous in vitro findings, the elevated surface pH in coeliac jejunum may affect digestive and absorptive processes occurring at the brush border.     

The ion sensitive field effect transistor (ISFET) pH electrode: a new sensor for long term ambulatory pH monitoring.

Intraluminal pH monitoring in man should be performed with disposable multichannel assemblies that allow recordings at multiple sites and prevent transmission of infection. Currently available glass electrodes are unsuitable for this purpose because of their size and price. We have thus constructed and tested a small, combined ion sensitive field effect transistor (ISFET) pH electrode incorporating an integral reference electrode. In vitro studies showed that both ISFET and glass electrodes (440-M4, Ingold, Switzerland) have a linear response over the pH range 1.3-8.0 and that they are comparable with regard to response time and 24 hour drift. Twenty one hour intragastric pH recordings were performed simultaneously in eight healthy volunteers using a glass electrode and an ISFET electrode, placed no more than 2 mm apart in a combined assembly. This was located in the gastric corpus under fluoroscopic control. The 21 hour pH curves recorded by each electrode type showed identical patterns: an early morning rise in pH with three meal-associated pH peaks lasting for about two to three hours. The means of the 21 hour pH medians were 2.09 and 2.07 as measured by the glass and the ISFET electrodes respectively. Thus, ISFETs are suitable for the construction of inexpensive and hence disposable multichannel pH monitoring assemblies of small diameter. Provided that they can be produced in large numbers with appropriate technical support, ISFETs have the potential to replace glass electrodes for long term monitoring of gastrointestinal luminal acidity.     

A new method for measurement of blood flow,pH, and transmucosal potential difference in rat gastroduodenal mucosa by endoscopy

A method was developed to measure the mucosal blood flow (BF), mucosal pH (pH), and transmucosal potential difference (PD) in various sites from the oral cavity to the duodenum without surgical operation or damage to the subject rats. These measurements were carried out by using three indicator electrodes, which were attached to the various sites through the suction channel of an endoscope. The hydrogen gas clearance method was used for the measurement of BF. BF values obtained at the fundic, pyloric, and duodenal regions were 119±17, 69.9±8.8, and 114±18 ml/min/100 g (mean±se), respectively. The pH values were lowest at the cardiac portion and the forestomach and highest at the duodenum. PD showed higher values at the stomach and lower values at the pharynx and duodenum. Using this technique, it was possible to measure the BF, pH, and PD repeatedly and safely at various sites in the same rat. Therefore, it was suggested that this method is useful in studying the physiological functions of the stomach and duodenum and the pathogenesis of gastroduodenal ulceration and that this method is applicable to measure the change of the above parameters in the healing process of gastric ulcer in rats.     

Effect of pH on bile salt injury to mouse gastric mucosa. A light- and electron-microscopic study.

Bile salts break the gastric mucosal barrier. To explain this, the suggestion has been made that bile salts may disrupt surface epithelial cell membranes or break the tight junctions between cells, but appropriate ultrastructural studies are lacking. We therefore instilled control and bile salt-containing solutions into the stomachs of fasted mice at pH, 1, 3, 5, AND 7. Taurocholate (pKa equals 1.8) caused mucosal injury only at pH 1, whereas glycochenodeoxycholate (pKa equals 4.2) injured the mucosa at pH 1 and 3. By electron microscopy, areas of mild mucosal injury were characterized by clumping of nuclear chromatin and loss of cytoplasmic density within surface mucous cells. The apical cell membranes and tight junctions remained intact. In areas of severe damage surface cells were ruptured but tight junctions still appeared unbroken. These studies indicate that acid pH markedly augments the damaging effects of bile salts on mouse gastric mucosa. Moreover, as an initial step in the mechanism of bile salt-induced gastric injury, the nonionized moiety of a given bile salt which exists below its pKa may be important in altering the gastric surface epithelial cell in a way which allows the ingress of bile salt and/or hydrogen ion to cause intracellular damage.     

Alkaline oesophageal reflux--an artefact due to oxygen corrosion of antimony pH electrodes.

Antimony electrodes are widely used for gastro-oesophageal pH monitoring. They are also sensitive to oxygen, however, especially at low PO2 levels, which are known to shift recorded values in the alkaline direction. This study, which compares antimony and glass electrodes for oesophageal pH monitoring in six adults, shows that values recorded by antimony electrodes are 2.1 +/- 0.8 pH units (mean +/- SD) higher than by glass electrodes (p < 0.001; n = 7642). A further 52 patients with suspected gastro-oesophageal reflux were investigated by 24-h pH monitoring by means of antimony electrodes. In these patients the oesophageal pH was higher than 8.0 for 7% of the time (range, 0-60%). The alkaline periods recorded with antimony electrodes were all protracted in time, smoothly increasing from a neutral pH, and did not correspond to a sudden increase in pH, which would be expected if alkaline reflux had occurred. It is concluded that high pH values obtained by antimony electrodes are due to the oxygen sensitivity of the electrodes. The diagnosis of alkaline reflux seems to be valid only when pH monitoring is performed with glass electrodes or when values obtained with antimony electrodes are adjusted for the influence of the oxygen tension in the oesophagus.     

Alkaline Oesophageal Reflux-An Artefact Due to Oxygen Corrosion of Antimony pH Electrodes

Antimony electrodes are widely used for gastro-oesophageal pH monitoring. They are also sensitive to oxygen, however, especially at low Po₂ levels, which are known to shift recorded values in the alkaline direction. This study, which compares antimony and glass electrodes for oesophageal pH monitoring in six adults, shows that values recorded by antimony electrodes are 2.1 ± 0.8 pH units (mean ± SD) higher than by glass electrodes (p < 0.001; n = 7642). A further 52 patients with suspected gastro-oesophageal reflux were investigated by 24-h pH monitoring by means of antimony electrodes. In these patients the oesophageal pH was higher than 8.0 for 7% of the time (range, 0–60%). The alkaline periods recorded with antimony electrodes were all protracted in time, smoothly increasing from a neutral pH, and did not correspond to a sudden increase in pH, which would be expected if alkaline reflux had occurred. It is concluded that high pH values obtained by antimony electrodes are due to the oxygen sensitivity of the electrodes. The diagnosis of alkaline reflux seems to be valid only when pH monitoring is performed with glass electrodes or when values obtained with antimony electrodes are adjusted for the influence of the oxygen tension in the oesophagus.     

Electrodes for 24 hours pH monitoring--a comparative study.

Three pH electrodes in clinical use were examined--(1) antimony electrode with remote reference electrode (Synectics 0011), (2) glass electrode with remote reference electrode (Microelectrodes Inc. MI 506) and (3) combined glass electrode with integral reference electrode (Radiometer GK2801C). In vitro studies showed that both glass electrodes were similar and superior to the antimony electrode with respect to response time, drift, and sensitivity. The effect of the siting of the reference electrode on the recorded pH was examined in five human volunteers. The pH reading using a remote skin reference electrode was higher by a mean of 0.3 pH units (range 0.0-0.6) in the stomach, lower by 0.65 pH units (0.5-0.8) in the duodenum and lower by 0.3 pH units (0.0-0.6) in the oesophagus than that simultaneously obtained with an intraluminal reference electrode. Buccal reference electrodes gave similar readings to skin. Combined reference and glass pH electrodes are recommended for 24-hour ambulatory pH monitoring.     

Development and evaluation in an ex vivo rat model of a technique for the endoscopic assessment of mucosal defense in man

We evaluated, in an ex vivo rat model, two electrodes suitable for use in man for the endoscopic assessment of luminal and juxtamucosal pH in the upper gastrointestinal tract. Luminal and mucosal pH measurements were performed under stereomicroscopic control in the exposed stomach of the anesthetized rat, using 0.5-mm and 1-mm immersion depth electrodes in the presence of various luminal pH values and after pre-exposure to the mucolytic agent N-acetylcysteine. Both electrodes consistently recorded lumen-to-mucosa pH gradients in the gastric corpus and antrum, the neutralizing zone being located over the surface of the mucosa. These gradients were dissipated on mucosal exposure to a highly acid luminal fluid and after pre-treatment with N-acetylcysteine. These studies indicate that these microelectrodes do, indeed, reliably record lumen-to-mucosa pH gradients and suggest that this method may prove a useful tool for the investigation of mucosal protection in man. Discrepancies between the size of the electrode and the depth of the mucus gel layer, which predispose to simultaneous sampling of luminal and mucosal pH, together with a slow response time, may, however, limit the sensitivity of the technique.     

Studies of the 'mucus-bicarbonate' barrier on rat fundic mucosa: the effects of luminal pH and a stable prostaglandin analogue.

Gastric mucosa may protect itself from acid peptic digestion by maintaining an alkaline barrier zone within the layer of mucus coating its surface. We have measured the pH gradient in the mucous layer in vivo, on the gastric mucosa of anaesthetised rats using antimony chloride micro pH electrodes. The maximum pH recordable adjacent to the epithelium was 7.43 +/- 0.56 (n = 8) when the luminal bathing solution pH was 2. Adjusting the luminal pH to 7.0 caused the maximal pH to rise to 7.88 (range 7.59 to 8.08), a value which is significantly higher than either luminal or reported intraepithelial pH and suggests that active secretion of alkali is involved. Pretreatment with 16-16-dimethyl prostaglandin E2 (20 micrograms subcutaneously) significantly increased the maximal intramucus pH to 7.89 +/- 0.45 (n = 8) when luminal pH was 2 and prevented the fall in intramucus pH induced by luminal aspirin (20 mM). It did not prevent falls in pH provoked by the mucolytic agent n-acetyl cysteine or by a high luminal activity (pH 1.4). These data indicate that an alkaline environment is maintained adjacent to gastric mucosa and that while this is enhanced by prostaglandin it may be compromised by high luminal acid concentrations or by removal of the support provided by mucus. These observations may be relevant to the mechanisms of gastric mucosal protection against acid peptic damage.     

Antimony and glass pH electrodes can be used interchangeably in 24-hour studies of gastric acidity

Antimony and glass pH electrodes show almost identical experimental errors in continuously measuring buffer solutions at constant temperature over 24 hr. These errors are lower than the nominal quantization error of the instruments and are not properly described by the 24- hr drift determination. The addition of food particles to the solutions can induce severe reading artifacts. The longer response time reported in vitroof antimony electrodes when moving from pH 1 to pH 7 (3.4 sec vs 0.8 sec with glass electrodes) is irrelevant during in vivopH-metry studies, because we found that the greatest absolute difference between raw fast acquired (4–6 sec) consecutive pH readings of two commonly used devices was 0.7 pH units in circadian profiles obtained from 413 subjects with various clinical conditions. In our in vivo studies, gastric acidity was monitored continuously with two side-by-side minielectrodes, which were variously combined (antimony-glass, A-G; antimony-antimony A1–A2; glass-glass, G1–G2) and applied on groups of 27 subjects matched for clinical condition. The 24-hr pH means and the 24-hr [H⁺] means calculated from the acidity profiles obtained with the three electrode combinations, lie on the identity line in each group. Using the Bland-Altman technique for assessing measurement agreement, the differences between the 24- hr pH means and the 24-hr [H⁺] means obtained with the three combined systems are similar (P=.903 and P=0.824, respectively) and their 95% confidence limits are comprised within the range (±) of the reading error of the measuring systems (namely, ±0.3 pH units and ±12 mmolliter in terms of [H⁺]). These data show that the 24-hr acidity indexes calculated from gastric pH recordings performed with two closely adjacent antimony and glass electrodes are similar, irrespective of their possible combinations. It can be concluded that antimony and glass electrodes provide equivalent results in vivo and can be used interchangeably in the clinical setting.     

Electrochemical improvement of the performance of PO2 electrodes.

Rotating ring-disc electrode studies have indicated that relatively large quantities of hydrogen peroxide ion, HO2-, are produced when oxygen is reduced at a platinum or gold polarographic electrode surface. The electrochemical reduction processes are improved and the quantity of HO2- is reduced by using alkaline buffer electrolytes (pH 10 to 11) and by polarising the electrode at voltages more negative than -0.9 V. The presence of HO2- in the electrolyte has been shown to be the cause of excessively long time response in both blood-gas and respiratory polarographic PO2 electrodes; electrode alinearity on micro-blood-gas PO2 electrodes has also been shown to be due to the absence of a plateau on the polarogram of electrodes when used with conventional electrolytes. The use of a high pH buffer and high negative voltage results in a long, flat plateau and a marked improvement in both electrode linearity and response time. This two-fold improvement in electrode performance holds true for both platinum and gold polarographic respiratory gas and blood-gas PO2 electrodes.     

Profound increase ofHelicobacter pylori urease activity in gastric antral mucosa at low pH

The effect of pH onH. pylori urease activity in its ecological niche was studied in gastric antral biopsy specimens. Specimens were incubated in 10 mmol/liter urea solutions at pH range 3.3–8.2. Activity of urease was studied by measuring production of ammonia and change in pH of the solutions. Urease activity was reduced at pH 8.2 (1424 ± 218 µmol/liter) but decreasing initial pH to neutral and acidic values resulted in significant maximal 6.5-fold increase in ammonia production (9491 ± 1073 µmol/liter,P<0.0005), which considerably raised the pH of the test solutions. Peak urease activity was between pH 5.0 and 7.0. In contrast to specimens incubated initially at pH 8.0, reincubation of washed specimens from solutions with initial pH 7.0 showed eightfold decreased urease activity. It is concluded that urease activity is markedly pH dependent with pH optima below the physiological mucosal surface pH. Furthermore, availability of urease is limited. Thus, an impaired gastric mucosal integrity allowing back diffusion of hydrogen ions may release urease activity, which might further weaken the mucus barrier and damage the gastric epithelium.This study was supported by the Deutsche Forschungsgemeinschaft (Mi 190/3).     

Bicarbonate and the regulation of ventilation

The regulation of ventilation involves a multifactorial control system with several feedback loops transmitting deviations from normal in pH, carbon dioxide tension (pCO₂) and oxygen tension (pO₂) to the control area. Variations in the size of the bicarbonate pool, caused by ventilatory or metabolic disturbances, can be expected to modify resting ventilation if hydrogen ion activity is the ultimate stimulus of the regulation of ventilation. A relationship between serum bicarbonate and resting ventilation can be identified in patients with stable acid-base disturbances including those in whom correction of the arterial blood pH was not achieved by respiratory adaptation. Why the pH in arterial blood is rarely returned to the normal range is not well understood. It may be an inadequacy of the control system, a “compromise” solution avoiding hypoxia in metabolic alkalosis or increasing work of breathing in metabolic acidosis, or a consequence of discrepancies in hydrogen ion activity in body fluids adjacent to and remote from the control site.Additional information about the role of bicarbonate in the control of ventilation may be obtained by measuring the response to carbon dioxide inhalation at varying extracellular bicarbonate concentrations. The increments in ventilation during inhalation of carbon dioxide are within individual limitations, inversely and exponentially related to the bicarbonate concentrations in blood.These observations are in accord with the concept that the extracellular bicarbonate concentration modulates resting ventilation and the ventilatory response to inhalation of fixed concentrations of carbon dioxide by acting as a determinant for the hydrogen ion activity within or adjacent to the central chemosensitive control area.     

Greatly increased mucosal nitric oxide in ulcerative colitis determined in situ by a novel nitric oxide-selective microelectrode

Although current nitric oxide (NO) electrodes are simple, selective and sensitive, they are fragile and hard to use in clinical studies of patients. By preparing an improved NO electroneedle that overcomes these defects, we directly measured mucosal NO concentrations in 11 patients (six male, five female; mean 26.0 years old) with ulcerative colitis (UC) and five normal volunteers (three male, two female; mean 28.3 years old) in situ . An electroneedle was inserted into colonic mucosa through a biopsy channel during colonoscopy. The information concerning the concentration of NO generated and the appearances of the colonic mucosa at the same site were obtained simultaneously. In the ulcerative colitis patients, NO concentrations were significantly increased at all 24 mucosal sites tested. These included sites where: there was an absence of visible inflammation (five sites); the mucosa was mildly inflamed (eight sites); the mucosa was moderately inflamed (five sites); or severely inflamed (six sites). The NO concentrations in ulcerative colitis patients were 12–72 times higher than the NO levels in normal controls (10 sites). At the same 10 sites in four ulcerative colitis patients, the high NO concentrations were decreased by 53% after glucocorticoid treatment. These data are consistent with those of previous studies utilizing different NO electrodes. Excess mucosal NO is generated from inducible NO synthase in the inflamed mucosa itself and the invading inflammatory cells. Our results suggested that mucosal NO could be a marker for the extent of inflammation and its various actions correlated with the pathogenesis, natural history and prognosis of UC. Using the NO microelectrode system reported here, the concentration of NO generated can be monitored in real-time while observing the mucosal condition at the same site during endoscopy. This novel NO electrode may contribute to understanding the role of NO in colonic mucosal inflammation.     

Stability of pH Gradients In Vivo across the Stomach in Helicobacter pylori Gastritis, Dyspepsia, and Health

A layer of water-insoluble mucus gel is secreted by the gastric epithelium, and is believed to form an important barrier to acid injury. It is postulated that Helicobacter pylori can alter pH gradients by damaging the mucus layer, but no data on pH gradients in vivo in patients with H. pylori gastritis have been published. We aimed to construct a map of mucus-bicarbonate layer pH gradients in health and disease. Fourteen healthy asymptomatic volunteers (mean age, 46 yr) and 14 symptomatic patients with non-ulcer dyspepsia (NUD) (mean age, 46 yr) were studied. A flexible pH microelectrode was passed through the biopsy channel of an endoscope; luminal readings and three mucosal surface pH readings were obtained from each of five specific gastric sites (fundus greater curve, body greater curve, antrum greater curve, antrum lesser curve, and antrum anterior wall) using standardized methodology. Gradients at each site were calculated (mean juxta mucosal pH minus luminal pH); pH electrode accuracy was tested in standard buffer solutions. Biopsies were obtained from each site to assess for H. pylori status. Among asymptomatic volunteers, 21% had H. pylori; in NUD, 50% were infected. There was a significant association between H. pylori and histological gastritis at each site. The overall mean (+/- SE) pH gradients in H. pylori-positive and -negative cases were similar, being 5.35 (+/- 0.06) and 5.26 (+/- 0.07), respectively. There was also no significant correlation between the histological gastritis score and the pH gradient at each gastric site. The pH gradients in healthy subjects (mean 5.31) and NUD (mean 5.29) were not significantly different. We conclude that pH gradients appear to remain stable throughout the stomach in healthy subjects and NUD, independent of H. pylori gastritis.     

Ambulatory 24-hour esophageal pH monitoring: why,when, and what to do

The incidence of gastroesophageal reflux disease (GERD) is increasing and if left untreated can lead to significant patient morbidity and even death. The disease results from the abnormal reflux of gastric contents into the distal esophagus causing symptoms in most and subsequent mucosal damage in some. Several investigations can be used to confirm the diagnosis, but most are dependent on the presence of sequelae and complications of the disease. The physiologic test of ambulatory 24-hour esophageal pH monitoring has proved to be the most sensitive and specific diagnostic investigation. It measures increased esophageal exposure to gastric juice by detecting the concentration of hydrogen ions (pH <4) in the distal esophagus. The technique measures gastric juice exposure at a point 5 cm above the manometrically determined upper border of the lower esophageal sphincter. The exposure is measured in components of frequency of reflux episodes, duration of reflux episodes, and accumulated exposure time. The components are integrated into a composite score, which is reproducible, gender and race independent, and correlates with the degree of esophageal epithelial damage determined histologically. The composite score has been shown to be the most reliable measurement of a therapeutic acid suppression regimen or an effective antireflux operation.     

Demonstration of a pH gradient across the mucus layer on the surface of human gastric mucosa in vitro.

In previous studies we have demonstrated a hydrogen ion concentration gradient across the mucus on rat and rabbit fundic mucosa, in vivo and in vitro respectively, observations which support the possibility of a 'mucus-bicarbonate' protective barrier. In the present studies we have demonstrated a similar gradient across the mucus on human gastric mucosa in vitro. The minimum mean hydrogen ion concentration at the mucus-epithelium interface was 1 . 1 X 10(-4) mM (pH 6 . 96, n = 10) when the luminal concentration was 5 . 6 mM (pH 2 . 25). Aspirin (10 mM) and N-acetyl cysteine (306 mM) (5%) increased the minimum intra-mucus hydrogen ion concentration and the gradient was overwhelmed by a luminal hydrogen ion concentration of 40 mM (pH 1 . 4). These results suggest that a hydrogen ion concentration gradient exists across the mucus on human gastric mucosa and that potential damaging agents may act by compromising one or other of th components of this 'mucus-alkaline', presumed 'mucus-bicarbonate', barrier.     

Effect of sodium taurocholate on the human gastric mucosa at acid and neutral pH's

This study was conducted to determine whether taurocholate alters human gastric function and structure at a neutral pH, when ionized, and to contrast this with its effect at an acid intraluminal pH, when pronated. Five fasted healthy subjects were studied on 4 days in random order. Net ion fluxes, mucosal damage (as quantitated endoscopically), and potential difference were measured. The control solution instilled into the stomach in the first, third, and fourth 15-min periods contained 200 ml of 100 mM HCl, 54 mM mannitol, and [14C]polyethylene glycol. Taurocholate (10 mM) was added to the control solution (pH 1.1) or citrate buffer (pH 7.0) during the second 15-min period. The effect of citrate buffer alone or control solution alone was also tested. Because hydrogen and sodium fluxes could not be quantitated at pH 7 in the presence of citrate buffer, the net ion fluxes during the 15 min immediately after exposure to the test agent were measured. At both pH 1.1 and 7.0 taurocholate produced similar and significant increases in net hydrogen ion flux (-1.7 +/- 0.4 and -1.8 +/- 0.3 mmol/15 min, respectively), net sodium ion flux (1.8 +/- 0.4 and 1.7 +/- 0.2 mmol/15 min, respectively), decreases in potential difference, and mucosal erosions. The net hydrogen ion fluxes were significantly greater than occurred after citrate buffer alone or the HCl control. The net sodium fluxes after taurocholate in citrate were significantly greater than the pH 1.1 acid control, but not citrate buffer alone. These findings indicate that pronated (pH 1.1) or ionized (pH 7.0) taurocholate significantly damaged the in vivo human gastric mucosa. Taurocholate at pH 7 could in part be responsible for the gastric mucosal injury that occurs in patients with bile reflux gastritis.     

Pancreatic proteases and intestinal mucosal injury after ischemia and reperfusion in the pig.

Intraluminal pancreatic proteases have been proposed to play a pathogenic role in the injury seen after ischemia and reperfusion of the small intestinal mucosa. Intestinal ischemia can be detected by indirect intramucosal pH measurements using tonometry. In this study, pigs were subjected to laparotomy and ligation of the pancreatic duct (n = 10) or a sham procedure (n = 10). Three weeks later, a standardized hemorrhagic shock was induced followed by retransfusion. Central hemodynamics, portal venous flow, and duodenal and small intestinal mucosal intramucosal pH were monitored. Samples were obtained from the small intestine for microscopic examination. A typical superficial mucosal injury developed in both groups of animals after reperfusion. However, the injury developed significantly later in the duct-ligated animals. No major differences in survival, splanchnic hemodynamics, or intramucosal pH between the groups were seen during hemorrhagic hypotension or after reperfusion. These data favor the concept that intraluminal pancreatic proteases are important for the rapid development of the mucosal reperfusion injury.     

Adequacy of disposable biopsy forceps for gastrointestinal endoscopy: a direct comparison with reusable forceps

Disposable plastic biopsy forceps were compared prospectively to reusable stainless steel forceps. Thirty consecutive patients underwent a total of 249 biopsies, 124 with the disposable forceps, and 125 with reusable forceps. Biopsy locations included the esophagus, stomach, small intestine, colon, and common bile duct. Specimens were compared microscopically to determine overall surface area, depth, adequacy, and diagnostic result. The disposable biopsy forceps yielded specimens which were 37% smaller when compared with the reusable forceps. In five of the comparisons, minor differences in histological findings were noted between the two groups of biopsy specimens, but these differences did not alter the pathological diagnosis. However, in three cases in which superficial specimens were obtained, an underlying carcinoma was missed with the disposable forceps. Our study documents the utility of disposable biopsy forceps for mucosal lesions. In addition, there were 11 mechanical failures in 38 biopsy attempts with the plastic biopsy forceps. These forceps appear to be limited in their capacity to obtain adequate specimens from firm tissue or when submucosal biopsy samples are required, and they will require refinements in design to duplicate specimen quality obtained by traditional reusable forceps. Disposable forceps are particularly suitable for biopsy of mucosal lesions in patients with possible communicable disease, and they should help to reduce cross-contamination in the gastroenterology laboratory.