Recurrent episodes of hypoglycemia, prostration, vomiting, and hepatomegaly were observed in an infant fed a carnitine-free soy formula. The extremely low plasma and urinary carnitine concentrations, elevated plasma free fatty acids, disproportionately low plasma beta hydroxybutyrate, and elevated urinary dicarboxylic acids, in the presence of a fatty liver, suggested that carnitine deficiency was the basis for this child's metabolic disturbance. When the infant was fed an enriched carnitine diet, remarkable clinical, biochemical, and histologic improvement was observed. The possibility that carnitine may be an essential nutrient for some infants is raised by the findings in this patient.