The role of total parenteral nutrition (TPN) in reducing toxicity related to cancer chemotherapy (CT) is presently a controversial issue. To evaluate the effectiveness of TPN in reducing CT-associated toxicity and correcting and preventing CT-related impairments of nutritional status, a prospective crossover controlled study was performed in 43 cancer patients (19 normally nourished and 24 malnourished) randomly divided into two groups (A and B). Group A patients received TPN concomitantly with the first course of chemotherapy, and the second course was administered 21 to 28 days later without TPN support; group B patients were treated in the opposite sequence. The rates of myelotoxicities and gastrointestinal toxicities after CT courses with or without TPN were essentially similar in normally nourished and malnourished patients. No changes in nutritional indexes were detected in normally nourished subjects after each course. Conversely, in undernourished subjects, prealbumin, retinol-binding protein, and nitrogen balance increased in CT+TPN courses (p < .02). In CT-only courses, undernourished subjects showed a decrease in prealbumin and nitrogen balance. Significant changes of nitrogen balance in CT vs CT+TPN courses were detected in malnourished subjects. TPN appears to be unable to reduce CT-associated toxicity. CT administration does not result in any impairment of the nutritional status in normally nourished cancer patients. From our study, it appears that TPN should be limited to severely malnourished neoplastic patients undergoing CT, because of its ability to prevent further impairment of nutritional status and to improve the nitrogen balance and the levels of fast-turnover visceral proteins.