During a randomized trial of total parenteral nutrition (TPN) in patients with small cell lung cancer, we evaluated the short- and long-term effects of 4 weeks of TPN on nutritional assessment parameters. All 119 patients who were accrued to the study received the same chemotherapy and radiotherapy protocol which extended over a 1-year period: 57 patients received TPN; and 62 served as controls. At base line, patients with greater than 5% pretreatment weight loss had significantly lower levels of serum albumin, total iron-binding capacity, and creatinine/height index. TPN administration led to a significant increase in mean caloric intake and weight compared with controls (P less than 0.0001). In the short-term study, body fat, as measured by triceps skinfold thickness, was maintained, and there was a small increase in arm muscle circumference. Serum albumin and hematocrit decreased but promptly returned to pretreatment levels when TPN was stopped. There were no long-term differences in any of the nutritional assessment parameters between the two groups.