We determined the effect of protein intake on weight gain and muscle function in the recovery phase after severe burns. Fifteen patients with deep burns between 30% to 50% of total body surface were studied over a 3 week period-after resolution of the hypermetabolic, catabolic state. All patients were studied in an acute rehabilitation hospital affiliated with the burn center. Nutritional profiles; weight gain; and muscle strength, measured by a physical therapy index (0 to 10)--10 being the greatest progress-were measured. All patients were provided a high-calorie, high-protein diet. Group 1 patients (n=8) also were provided a standard nutrient supplement to maintain caloric intake at 30 to 35 kcal/kg/day and to maintain protein intake at 1.3 to 1.5 g/kg/day. Group 2 patients (n=7) were provided a high-calorie, high-protein diet plus a protein hydrolysate (70 g/day) that provided a protein intake of 1.7 to 2 g/kg/day. Group 1 patients averaged a 1 to 1.5 pound weight gain per week or four pounds during three weeks. Their physical therapy index at three weeks of 4+/-0.5 indicated adequate improvement in strength and endurance. Group 2 patients averaged 2.5 to 3 pounds weight gain per week or 8.5 pounds during three weeks. Their physical therapy index of 7+/-0.7 indicated marked gains in muscle strength. Both measurements were significantly higher than those of Group 1. We conclude that increased protein intake by means of adding a protein hydrolysate increases the rate of restoration of body weight and muscle function.