Ileal endogenous amino acid (IEAA) and total amino acid (TAA) flow (mg/kg of DM intake) in turkey poults and broiler chicks at 3 ages (5, 15, and 21 d) were compared by feeding a N-free diet (NFD) or graded levels of casein (highly digestible protein, HDP). The semipurified diets contained 0 (NFD), 50, 100, or 150 g of casein/kg of diet as the only source of amino acids. Each diet was fed to 6 replicate cages containing 30 (5 d), 10 (15 d), or 8 (21 d) birds per cage for 5 d prior to the collection of ileal digesta. At d 5, IEAA and TAA flow in poults fed the NFD, 50, and 100 g of casein/kg of diet was higher (P < 0.05) than in chicks. The IEAA flows within and between both species on d 15 and 21 were not different. Similar trends were observed for the HDP diets (50, 100, or 150 g of casein/kg of diet). An interaction (P < 0.05) between species and age was observed for most of the amino acids for all treatments. The results from this study suggest that at d 5, poults have significantly higher concentration of IEAA and TAA output relative to chicks. However, by d 15 and 21, there were no species differences in IEAA or TAA flow. These results also showed that IEAA flow is species and age dependent. The increased IEAA flow observed at d 5 should be taken into consideration when formulating starter diets on a digestible amino acid basis.