Two studies evaluated the effects of soya bean trypsin inhibitor concentrate (STIC) on early stages of pancreatic carcinogenesis in Wistar rats. In experiment 1, the effects of a 3-month administration of diets containing 3.7% STIC were compared with the effects of administration of diets containing 20% corn oil, in rats pretreated with a single azaserine injection sufficient to initiate putative preneoplastic atypical acinar cell foci. Experiment 2 investigated the capacity of STIC to initiate pancreatic carcinogenesis. Diets containing 3.7% STIC were fed for 4 wk, then diets containing either 5 or 20% corn oil were fed for 3 months. Pancreases were quantitatively evaluated for foci. All groups of azaserine-initiated rats had large numbers of atypical acinar cell foci per cm3 of pancreas. Of these, the group fed 3.7% STIC had pancreatic foci that occupied a significantly greater (P less than 0.01) percentage volume of pancreas than did groups fed 20% corn oil or control diets, which contained 5% corn oil and no added trypsin inhibitor. Very few or no foci were observed in all other groups of either experiment 1 or 2. STIC had a much greater effect on the growth of azaserine-induced lesions than did corn oil. STIC alone did not appear to initiate pancreatic lesions.