Protein--calorie malnutrition is the single most common secondary diagnosis in patients with cancer, and is a direct consequence of the anorexia of malignancy and altered host metabolism induced by tumor. One hundred and sixty-one cancer patients were nutritionally assessed prior to receiving oncological therapy (surgery, chemotherapy, and/or radiation therapy). Eighty-four percent (27/32) of the patients who were initially anergic became immunocompetent with nutritional therapy and had a mortality rate of 11% as compared to 100% mortality in the 5 patients who remained anergic throughout their hospital stay. Thirty-nine percent (14/36) of the patients initially immune competent became anergic and had a concomitant mortality rate of 50% vs. a mortality rate of only 14% in the 22 patients whose immune function was preserved (p less than 0.05). Those patients who were discharged at the completion of their therapy also exhibited a higher initial serum albumin (3.5 +/- 0.1 vs. 3.1 +/- 0.1 g/dl, p less than 0.001) and serum transferrin (149 +/- 7 vs. 125 +/- 7 mg/dl, p less than 0.05). A significant increase (p less than 0.025) occurred in serum transferrin (delta 23 +/- 9 mg/dl) after 3 or more weeks of nutritional support. The detection and treatment of protein--calorie malnutrition prior to or in conjunction with oncological therapy has been associated with a decrease in mortality rate.