The amino acid requirements of poultry are influenced by dietary, environmental and genetic factors. Therefore it is almost impossible to address all these factors in determining amino acid requirements. This problem can be overcome by expressing the amino acid requirements as ratios to lysine. In this concept it is assumed that the ideal ratio of amino acids to lysine remains largely unaffected by dietary, environmental and genetic factors. In this paper the present knowledge about the ideal amino acid profile in diets for layers and broiler chicks is discussed. Based on digestible amino acids, the ideal amino acid ratio relative to lysine in layer diets was estimated to be 84 per cent methionine plus cystine, 64 per cent threonine, 18 per cent tryptophan, 81 per cent valine and 74 per cent isoleucine. In broiler chick diets the ideal amino acid ratio relative to lysine was estimated to be approximately 75 per cent methionine plus cystine, 65 per cent threonine, 18 per cent tryptophan, 110 per cent arginine, 80 per cent valine and 70 per cent isoleucine on a digestible basis.