Findings in a 1-month-old male infant with Wolman's disease, a rare autosomal defect characterized by intractable diarrhea and severe malabsorption, are described. Investigations in this case focused on the digestive and absorptive functions of the jejunum using histological, biochemical, and electrophysiological methods. The intestinal villi were found to be distorted and club-shaped as a result of the infiltration of foam cells into the lamina propria of the mucosa. The microvilli of the epithelial cells were found on electron microscopy to be markedly shortened and irregular, and had a severe impairment of disaccharidase activity. Documentation of the loss of the sugar- and amino acid-evoked potential differences in the jejunum confirmed the severity of intestinal malabsorption. These observations indicate that the intestinal damage in Wolman's disease is so severe as virtually to exclude the absorption of any form of enteral nutrition. Despite the administration of i.v. hyperalimentation, the infant died of hepatic failure at the age of 6 months.