In order to determine if intermittent hormonal therapy might prove to be beneficial in the treatment of prostatic cancer, animals bearing the Dunning R3327H prostatic adenocarcinoma were castrated and intermittently subjected to hormonal stimulation by means of indwelling silastic testosterone-filled implants. The growth of these tumors, as measured by increases in volume, was compared to that of a castrate control group, a chronic implant group and an intact control group. By the end of an initial 49 day experimental period there was no significant growth reduction with the intermittent stimulation group as compared to the implanted control or intact groups. The castrate group had a significant lower rate of growth than any other group. The incidence of massive tumor growth or tumor necrosis was significantly lower in the castrate group than the other groups by the end of the 16 week experimental period. Intermittent hormonal therapy is clearly inferior to early castration in preventing tumor growth; furthermore it does not appear to offer any growth-retarding advantages when compared to delayed hormone therapy. The most effective growth-retarding technique for the Dunning R3327H hormone dependent prostatic adenocarcinoma is early castration.