Four experiments were conducted to determine the arginine and lysine requirements of male chickens for 2- to 3-wk intervals from the time of hatching until 8 wk of age. Weight gain, breast muscle growth, and feed efficiency were used as response for each interval. Dietary requirements for lysine and arginine were estimated by broken-line regression analysis of responses to six or seven dietary levels of each amino acid. Dietary crude protein levels were 22, 21, 20, and 18% in four consecutive experiments from 0 to 2, 2 to 4, 3 to 6, and 5 to 8 wk of age. An occasional estimate of requirement was not determined (ND) because the response did not conform to the regression model. The values for lysine and arginine requirements determined from breast muscle gain (weight gain of pectoralis major plus pectoralis minor) were not significantly higher than those from body weight gain. However, they tended to be higher than for feed efficiency for 0-to-2 and 2-to-4-wk-old broilers. Lysine and arginine requirements, as percentages of total amino acid in the diet, for maximum breast muscle growth were, respectively, 1.32+/-0.01% and 1.27+/-0.00% to 2 wk of age, 1.21+/-0.06% and ND for 2 to 4 wk of age, 0.99+/-0.02% and 0.97+/-0.02% for 3 to 6 wk of age, and 0.81+/-0.01% and 0.83+/-0.02% for 5 to 8 wk of age. Calculated digestible lysine and arginine requirements were, respectively, 1.24 and 1.19% to 2 wk of age, 1.11% and ND for 2 to 4 wk of age, 0.92% and 0.91% for 3 to 6 wk of age, and 0.75 and 0.78% for 5 to 8 wk of age. The requirements for lysine and arginine were similar except for the earliest age group for which the lysine requirement appeared to be slightly higher than that of arginine.