Previous work in our laboratory and others suggests that protein malnutrition plays an important role in the pathogenesis of hepatic steatosis and dysfunction which characteristically appears after jejunoileal bypass for morbid obesity. Postoperative protein-calorie malnutrition is at least in part a consequence of diminished intestinal absorption of free amino acids. In an attempt to prevent liver disease, six morbidly obese patients were orally supplemented with essential amino acids for 4 months after surgery. Oral amino acid supplementation only partially influenced protein malnutrition and had no effect on deterioration of hepatic morphology and dysfunction. Although this mode of therapy appears to be ineffective in preventing postoperative liver abnormalities, other studies suggest that oral oligopeptide supplementation and parenteral administration of amino acids are beneficial. In addition to protein deificiency, other factors which may contribute to the development of liver disease are reviewed.