Metabolic studies were performed in 8 of 14 patients with severe anorexia nervosa (AN) before and after nutritional therapy. The decrease of lean body mass, as judged by the low values of the creatinine-height index (CHI), and the normal levels of visceral proteins demonstrate the marasmic pattern of undernutrition in AN. Low 24-hour urinary 3-methylhistidine and urea levels agree with adaptation to malnutrition by decreasing in muscular breakdown. With enteral and oral feeding, weight gain was impressive and CHI reached normal values; 3-methylhistidine increased, reflecting enhancement of myofibrillar protein metabolism. By the end of refeeding, the levels of rapid-turnover proteins (prealbumin, retinol-binding protein) were higher than normal. Thus enteral feeding appears to be an efficient treatment of malnutrition in severe AN.