Compared with the control chicks, the chicks fed ad libitum with the arginine-deficient diet consumed less feed and less metabolizable energy, and subsequently, gained less weight and less energy, and showed lower gross energetic efficiency. When the same amounts of the control and arginine-deficient diets were tube-fed, the arginine-deficient chicks gained less body weight and retained less protein energy and more fat energy than the control chicks. Total energy retention was not affected by arginine deficiency and was simply proportional to the ME intake. Arginine deficiency affected neither the maintenance ME requirement nor the net efficiency of ME utilization for energy gain. These results show that the decreased energy retention in the chicks fed ad libitum the arginine-deficient diet is associated with the decreased feed intake.Acknowledgement The authors wish to express their thanks to Mr. H. SAITO for his technical assistance.