A randomized study was performed in advanced cancer to test the effectiveness of total parenteral nutrition (TPN) in maintaining and improving nutrition, to examine the effects of TPN on tumor growth, and to determine if TPN altered chemotherapy response rates, treatment tolerance, and survival. Forty-five patients on identical chemotherapy were randomized to TPN versus ad libitum feeding. TPN was well tolerated. No clinical or tumor marker evidence suggesting neoplastic growth stimulation was obtained. Chemotherapy-related complications and chemotherapy responses did not differ between the two groups. TPN had little effect on performance status. TPN patients gained an average of 2.8 kg before chemotherapy, but triceps skinfold and mid-arm muscle area did not change significantly during TPN. Survival did not improve with TPN. We conclude that current techniques of TPN are of limited benefit in advanced colon cancer. A small subset of patients with short-gut malabsorption may be helped. Further study is needed to determine the mechanisms of cancer undernutrition and to refine nutritional supplementation techniques on the basis of these mechanisms.