Carnitine is necessary for the transport of long-chain fatty acids across the mitochondrial membrane. Carnitine is derived from the diet and from endogenous synthesis from lysine and methionine. About 98% of the body's carnitine pool is located in skeletal muscle tissue. Skeletal muscle carnitine levels were determined in two groups of malnourished patients, eight patients with anorexia nervosa with a weight loss of 32.4% +/- 1.8 (mean +/- SEM) and six surgical patients with major gastrointestinal disorders and a weight loss of 15.2% +/- 2.7. Their hepatic and kidney functions were normal. On admission, the muscle carnitine levels were 16.9 +/- 4.0 mumol/g dry weight (mean +/- SD) for the surgical patients and 20.8 +/- 5.0 mumol/g dry weight for the anorexia nervosa patients, which corresponded to carnitine levels seen in healthy subjects. No statistical significance was found between the two groups. Total parenteral nutrition was given to the surgical patients for 2 weeks and to the anorexia nervosa patients for 3-5 weeks. No statistical difference in muscle carnitine levels was found in either group after nutritional support. These malnourished patients had no decreased muscle carnitine levels on admission and maintained them during several weeks of total parenteral nutrition.