Two assays were conducted to (1) determine if the chick has a lesser requirement for a methionine-cystine combination than for all methionine and (2) evaluate the efficacies of methionine, cystine and cysteine when added to a cystine-void crystalline amino acid diet. When the total sulfur amino acid (TSAA) requirement was expressed as a percent of the diet, the need for a methionine-cystine combination was less than for all methionine. This did not appear to be a result of metabolic inefficiency but rather due to the fact that feed intake maximized at a lesser concentration with the sulfur amino acid combination than with all methionine. The molar efficacies of methionine, ½ cystine and cysteine were the same as indicated by slope-ratio.