Hydrazine sulfate was found to be a potent inhibitor of the Waker 256 intramuscular carcinoma in rats. In dosages ranging from 4 mg/kg to 128 mg/kg rat body weight, the tumor inhibitions ranged from 28% to 94%, respectively. Only at a dose, of 128 mg/kg was there any drug-induced mortality; there was indication of drug-induced weight loss at the 64 mg/kg dosage level. At dosages ranging from below 64 mg/kg to 4 mg/kg there was no manifest form of toxicity (i.e., mortality or weight loss), even though tumor inhibition was still high and statistically significant. Hydrazine sulfate is a known PEP KC (phosphoenolpyruvate carboxykinase) inhibitor, and this mechanism is thought to be responsible for the tumor inhibition produced. It is suggested that direct experimental evidence of such a mechanism of action would implicate an entire new chemotherapy, based on the interruption of cachexia via gluconeogenesis inhibition.