The results of a previous 4-mo study in azaserine-treated rats and BOP-treated hamsters indicated that orchiectomy inhibited pancreatic growth and development of putative preneoplastic lesions in the exocrine pancreas of rats but not hamsters. This 12-mo study was carried out to investigate the effects of orchiectomy, alone and in combination with testosterone, and of treatment with cyproterone acetate on pancreatic carcinogenesis in azaserine-treated rats and BOP-treated hamsters. Treatment started 4 mo after injection of the carcinogen. In orchiectomized rats, pancreatic wt was lower than in controls, whereas pancreatic wt of orchiectomized rats treated with testosterone was similar to that of controls. Both orchiectomy and cyproterone acetate caused a decrease in body wt gain and had an inhibitory effect on pancreatic carcinogenesis. Testosterone treatment did not influence the inhibitory effects of orchiectomy on body wt gain and on pancreatic carcinogenesis. In hamsters, neither orchiectomy, alone or in combination with testosterone, nor cyproterone acetate (CA) affected pancreatic growth or pancreatic carcinogenesis. This study indicates that testosterone plays a minor role in the development of pancreatic tumors induced in rats by azaserine but not in that of pancreatic tumors induced in hamsters by BOP.