his study was designed to analyze the effect of two pancreaticotrophic peptides on pancreatic carcinogenesis in the azaserine-rat model. The rats were treated with bombesin or caerulein for 16 weeks after initiation with azaserine. Two-week-old Lewis rats were given injections of a single dose of azaserine (30 mg/kg) and the control pups received an injection of saline. They were divided into ten groups for peptide treatment as follows: Group 1, azaserine-saline; Group 2, azaserine-bombesin, 10 µg/kg; Group 3, azaserine-bombesin, 30 µg/kg; Group 4, azaserine-caerulein, 5 µg/kg; Group 5, azaserine-caerulein, 15 µg/kg; Group 6, control-saline; Group 7, control-bombesin, 10 µg/kg; Group 8, control-bombesin, 30 µg/kg; Group 9, control-caerulein, 5 µg/kg; and Group 10, control-caerulein, 15 µg/kg. At 3 weeks of age, they were weaned. Peptides or saline were injected 3 consecutive days a week for 16 weeks. Rats were autopsied 4 months after the administration of azaserine. Pancreatic weight was increased by bombesin and decreased by caerulein treatment. Quantitative histological analysis of azaserine-induced atypical acinar cell nodules in the pancreas showed that the size and number of atypical acinar cell nodules were increased in both bombesin- and caerulein-treated groups. Thus, these peptides appear to stimulate the growth of preneoplastic acinar cell lesions.