The effects of concomitant administration of a synthetic trypsin inhibitor (camostat) on pancreatic carcinogenesis in hamsters treated with N-nitrosobis(2-oxopropy1)amine (BOP) were investigated. Thirty-two female Syrian golden hamsters were given weekly 10 mg/kg S.C. injections of BOP for 5 weeks while simultaneously receiving a 500 ppm camostat diet (BOP + camostat group). Additional groups of 30 animals received either the S.C. injections of BOP (BOP group), or the 500 ppm camostat diet (camostat group) during the same 5-week period. Thirty weeks after the first BOP administration, the incidence of pancreatic adenocarcinomas in the BOP + camostat group was significantly lower than in the group administered BOP only (p < 0.05). Similarly, the total numbers of pancreatic adenocarcinomas or dysplas-tic lesions were significantly decreased in the BOP + camostat group as compared with the BOP group (p < 0.01). None of the animals receiving camostat alone developed any adenocarcinomas or dysplastic lesions of the pancreas. The results of the present experiments clearly show that camostat can inhibit induction of hamster pancreatic ductal neoplasms when administered simultaneously with BOP.