y composition was studied in 31 patients receiving chemotherapy for small-cell lung cancer. Patients were randomly assigned to receive either 4 weeks of total parenteral nutrition (study group) or to continue a self-regulated oral diet (control group). The relationship between height and total body nitrogen was altered initially for patients who had lost more than 5% of body weight. During the 4 weeks of parenteral nutrition, body weight, total body fat, and total body potassium, but not total body nitrogen, increased significantly in the study group (p less than 0.001). However, after parenteral nutrition was stopped, body weight and potassium levels in the study group fell significantly and to the same extent as in the control group. Nitrogen levels showed an overall fall in the 32 weeks of observation for both groups. After the period of parenteral nutrition, the decrease in body fat was significantly greater in the control group than in the study group (p less than 0.05). Thus, parenteral nutrition increased body fat and total body potassium, but not total body nitrogen.