Two experiments were conducted to test the hypothesis that standardized ileal digestibility (SID) of AA by growing pigs is not influenced by dietary AA. In Exp. 1, thirty cannulated pigs (BW:31.4 ± 3.9 kg) were allotted to 5 diets. Four diets were formulated to contain 4.7 to 30.4% CP, by including 10, 30, 50, or 70% soybean meal. An N-free diet was used to determine the basal endogenous losses of CP and AA. The model included diet as a fixed variable and polynomial contrasts were used to test linear and quadratic effects of dietary AA. The SID of CP, Lys, Phe, and Thr decreased linearly (P < 0.05) as dietary AA increased (Table 1). However, this effect was primarily a result of the SID of AA in the diet containing 30.4% CP and the SID of CP and most AA was not affected by dietary AA if diets contained 4.7 to 22.1% CP. In Exp. 2, twenty-four cannulated pigs (BW:22.8 ± 1.7 kg) were used. Pigs were allotted to a quadruplicated 6 × 2 Youden square design with 6 diets and 2 periods. Five diets were formulated to contain 6.8 to 31.8% CP, by including 10, 20, 30, 40, or 50% soy protein concentrate. An N-free diet was also used. Data were analyzed as for Exp. 1. The SID of His and Lys decreased quadratically (P < 0.05) with increased dietary AA (Table 2). However, if dietary CP was 26.6% or less, no effect of dietary AA on SID of CP and most indispensable AA was observed.