The prostate of the rat has several lobes which have variable responsiveness to estrogens and testosterone. Testosterone is a major stimulant of cell proliferation in the prostate. Chemical carcinogenesis models in the rat prostate have taken advantage of administering the carcinogen during the peak proliferative period following testosterone administration with subsequent testosterone administered to continue the proliferative stimulus. Invasive adenocarcinomas of the prostate have been induced utilizing such methods.