Using 40 White Leghorn male chicks, variations of protein and energy intakes were determined on a separate protein feeding system, which gave free choice of intake of a protein and a protein free diet. Isolated soybean protein and milk casein were used as protein sources. Body weight gain for 2 weeks on the separate feeding system was the same as that on the corresponding mixed diet system (20% protein diet) for both proteins, although body weight gain on milk casein was less than that on soybean protein. Protein intakes on the separate protein feeding systems were slightly less than those on the mixed diets when either soybean protein and milk casein was used. Energy intake of chicks fed soybean protein by the separate feeding system was less than that of chicks on the mixed diet feeding system. The reverse was true in the case of milk casein. Protein and energy utilization ratios of chicks fed by the separate feeding system were 89 and 90% on the soybean protein mixed diet. From these results it seems that a separate protein feeding system can be effectively used in methods of estimation of growth, feed intake and other nutritional studies with chicks.