Protein requirement studies in man generally avoid deficient dietary energy intakes because they decrease the efficiency of nitrogen utilization, but the opposite effect of excess dietary energy is usually overlooked. Four young men were fed the 1973 FAO/WHO safe level of egg protein (0.57 g/kg) at several levels of dietary energy. The data indicate that a significant proportion of the population may require excess energy intakes to maintain nitrogen balance at this level of dietary protein. Variations in dietary energy ranging from submaintenance to 15 to 20% above estimated maintenance needs altered net egg protein utilization in three subjects by 2 to 4.5 units/kcal per kg body wt.