Severe protein-energy undernutrition is a frequent finding among chronically ill patients. Its causes are anorexia, hypermetabolism, and malabsorption. Adverse consequences include impaired cell-mediated immunity, increased susceptibility to infection, poor wound healing, weakness, and death. Spontaneous oral intake is inadequate in patients with this disorder, and therapeutic maintenance or repletion alimentation is needed. Enteral hyperalimentation is the method of choice, if tolerated. A successful treatment program usually requires a small-bore, flexible nasoenteral tube, appropriate feeding solution, and constant flow delivery of nutrient. If only partial dietary requirements are tolerated enterally, peripheral intravenous nutrient solutions can often supply the deficit. Although not suitable for all patients, enteral hyperalimentation is more physiologic, safer, easier, and more economical than central venous hyperalimentation. It would be well tolerated by many patients who now receive nutritional repletion by the latter method.