The effect of hydrolysis was determined by a pancreatic enzyme preparation (Viokase) on a series of diets available for enteral nutrition. The increase in osmolality resulting from digestion by Viokase was measured. Small amounts produced very rapid increase in osmolality in almost all diets evaluated. Neither incubation at 37°C nor the addition of larger amounts of the pancreatic enzyme preparation produced further substantital increases in osmolality. The importance of proper and adequate nutritional support of acutely and chronically ill patients is discussed, and a guideline for the choice of diets, route of delivery, and concentration of diets is suggested.