After the injection of the potent carcinogen 9,10-dimethyl-1,2-benzanthracene (DMBA) male rats (Fisher/Furth), mice (Strong A/J), and Golden hamsters, which had been previously conditioned by castration and in which the prostate had become histologically atrophic, developed tumors consistent with prostatic adenocarcinoma. One month after castration, intravenous injections of DMBA were given in the vena cava or jugular vein once a month for 3 months. Three to four months later, histologic evidence of prostate adenocarcinoma was consistently found in each of the groups of castrated animals (11 rats, 22 mice, and 11 hamsters) which survived the experiment. The glands were enlarged grossly and ureteral obstructions were also noted. Metastasis to the lung also occurred in five mice, three rats, and one hamster.