Recipient survival in canine pancreatic allotransplantation was significantly prolonged when animals were treated with 5-fluorouracil in combination with low-dose azathioprine. Untreated dogs and those receiving only azathioprine survived for only short periods of time, and pancreatitis was frequently encountered. In contrast, animals treated with 5-fluorouracil were protected from pancreatitis and survived an average of almost three weeks.