Prostate cancer remains the most commonly diagnosed cancer in American males and is the second leading cause of cancer death in this group. Hydrazine sulfate, an inhibitor of gluconeogenesis, has been proposed as a means to improve nutritional status and improve survival in patients with solid tumors. We investigated the effects of hydrazine sulfate on both in vitro and in vivo models of prostate cancer. We examined the cytotoxicity of hydrazine sulfate in both human (LNCaP and PC-3) and animal (MAT-LyLu) prostate cancer cell lines. No growth inhibition was observed. In vivo, hydrazine sulfate did not suppress the growth of implanted Dunning rat prostate MAT-LyLu cells. Hydrazine sulfate does not have activity in these models of prostate cancer and may not be an appropriate therapy for patients with prostate cancer.