A proposed role for the hypothesized toxohormone/s (Vasopressin, Prostaglandin E2 and TNF-Cachectin) in the development and maintenance of cancer cachexia was investigated in rats bearing the Walker 256 carcinosarcoma. Elevated levels of arginine vasopressin and prostaglandin E2 in the plasma and urine were associated with reduced hepatic ketogenesis, fatty acid oxidation and increased fatty acid esterification. The oxidation of branched chain amino acids by the muscle tissue of tumour bearing rats was increased and attributed to the enhanced activity of muscle branched chain keto-acid dehydrogenase. Concerted actions by the triology of factors (AVP, PGE2, Cachectin-TNF) are proposed to instigate a sequence of reactivities that lead to the clinical symptoms of muscle and adipose tissue wasting, together with the negative nitrogen balance characteristic of the cachectic state.