In view of the world shortage of dietary protein, and the fact that yeast protein can be used to replace half of other proteins in the diet of chicks and rats, the possibility of improving the nutritional value of yeast by raising its protein and methionine content was investigated. Baker's and brewer's yeasts are known to be deficient in methionine and cystine, although literature data on percentages present vary greatly. The methionine content of seven commercial yeasts was found to vary from 0.48 to 0.75% on a dry basis. A fat yeast, Rhodototula gracilis, contained 1.00% of methionine, which is about 20% higher than the commercial Saccharomyces species and nearly double that of the Torula type (0.54%). The protein content and methionine value of yeast were guilliermondii, C. zeylanoides, Debaryomyces