An experiment was conducted to examine the possibility that the carcinogenic effect on the pancreas of streptozotocin (SZ) and N-nitrosobis(2-oxopropyl)amine (BOP) is based on similar mechanisms; groups of outbred Syrian golden hamsters were treated with SZ (single iv injection, 30 mg/kg body wt) alone, BOP alone (single sc injection, 10 mg/kg body wt), and SZ and BOP simultaneously. The experiment was terminated 52 weeks after treatment began. Of the hamsters treated with SZ alone, 44% developed islet cell tumors, most of which were of pleomorphic cell types. In addition, 40% of the hamsters developed pseudoductules and 12% developed ductular adenomas. The carcinogenicity of SZ for the exocrine pancreas was further indicated by induction of ductular carcinomas by SZ plus BOP, the incidence of which was significantly higher (P less than .0001) than that induced by BOP alone.