Possible promotion of MNNG-induced gastrointestinal carcinogenicity was evaluated in male Wistar rats exposed to unconjugated bile acid given as gavage or as obtained through truncal vagotomy plus pyloroplasty. No significant difference was found compared with the relevant control groups. Even though gastroduodenal erosions were found more frequently in the bile acid gavage and MNNG groups than in MNNG-treated controls, secondary deconjugated bile acids apparently did not reach optimal promoting concentrations. In contrast to partial gastrectomy, vagotomy and pyloroplasty does not increase the tumor yield in the rat.