A patient with repeated episodes of a Reye-like syndrome was studied. Serum and muscle carnitine levels were normal, but there was an apparent accumulation of muscle lipid and glycogen. Ragged-red fibers were present in the muscle. Prolonged fasting (20 hours) induced hypoglycemia, lactic acidosis, an increase in free fatty acids, and hyperammonemia. There was an accompanying sizeable reduction in the serum free carnitine level. Fasting with L-carnitine administration resulted in milder changes in these laboratory measures. Administration of L-carnitine, (100 mg/kg/day) led to clinical improvement as evidenced by fewer attacks and a normal Gowers sign.