Five experiments designed for various purposes [mainly for the study of colon carcinogenesis in inbred F344 male rats given sc injections of 3,2'-dimethyl-4-aminobiphenyl (DMAB)] were reviewed as to the production and presence of neoplastic lesions of the prostate gland. The overall incidence of prostate proliferative lesions among 293 animals exposed to DMAB was 32% (95 animals). Early in situ carcinomas were present in 66 animals, larger intra-acinar carcinomas in situ in 28, and invasive carcinoma in 1. None of the control animals in these studies exhibited prostate neoplasms. The conclusion, therefore, is that DMAB can induce adenocarcinomas in the rat prostate gland.