The clinical syndrome of cachexia is characterized by anorexia, continued losses of lean body mass, and altered carbohydrate and lipid metabolism. As early as the 1930s, this "chronic wasting" syndrome had been identified as the most frequent immediate cause of death in patients with cancer [Warren: Am J Med Sci 184:610-619, 1932]. At present, controversy remains as to the benefit of supplemental parenteral or enteral feedings in the nutritional repletion of cachectic cancer patients, since only selected patient groups have demonstrated clear benefit from their administration [Copeland et al.: Cancer 43:2108-2116, 1979; Copeland et al.: Cancer Res 37:2451-2456, 1977; Terepka and Waterhouse: Am J Med 20:225-238, 1956]. Despite having these advanced nutritional modalities firmly in our therapeutic armamentarium, the progression of cachexia in the nutritionally depleted cancer patient often continues unabated, and our ability to intervene successfully remains limited. This review proposes that host: tumor interactions lead to a nonspecific inflammatory response mediated in part by the chronic production and release of proinflammatory cytokines, including interleukin-1, tumor necrosis factor alpha, interleukin-6 and interferon-gamma, which antagonize the anabolic signals associated with enteral and parenteral nutrition support. Cytokine-mediated alterations can explain the inability of adequate dietary nitrogen and calories to result in lean tissue repletion. Based on this proposal, interrupting proinflammatory cytokine production or target organ action may be an appropriate therapeutic objective to improve nutrient utilization in patients with tumors.