A series of feeding experiments was conducted in aquaria to determine the quantitative requirements of the 10 essential amino acids for growth of young Nile tilapia (Oreochromis niloticus). The test diets contained casein and gelatin supplemented by crystalline L-amino acids to provide an amino acid profile similar to 28% whole egg protein except for the test amino acid. Each set of test diets consisted of seven isonitrogenous diets containing varying levels of the amino acid to be tested. Weight gains analyzed by the broken line regression method indicated the following requirements as a percentage of the dietary protein: lysine, 5.12; arginine, 4.20; histidine, 1.72; valine, 2.80; leucine, 3.39; isoleucine, 3.11; threonine, 3.75; tryptophan, 1.00; methionine with cystine (0.54% of the protein), 3.21; and phenylalanine with tyrosine (1.79% of the protein), 5.54.