The metabolic responses associated with the tumor-bearing state, as compared to states of sepsis and prolonged starvation, were examined. Tumor-bearing rats manifested significant elevation of triglycerides, significant reduction of glucose and insulin levels, significantly increased plasma skeletal muscle proteolysis-inducing activity, and an unchanged hepatic protein synthetic activity compared to control rats. Prolonged starvation produced an adaptation characterized by significant hypoglycemia and hypoinsulinemia, reduced hepatic protein synthesis, and increased peripheral protolysis compared to controls. Septic animals had glucose, insulin, and lipid levels similar to control animals but had increased hepatic protein synthesis. Each state manifested its own unique metabolic response compared to controls. It appears that the metabolic consequences of cancer in this sarcoma rat model is different than septic and prolonged starvation states.