Two baker's and two brewer's yeast strains ofSaccharomyces cerevisiaewere compared. Regarding their cell composition there was almost no difference in proteins and nucleic acids. Differences were observed in total lipid amounts as well as in lipid composition. Baker's yeasts contained only about one half as much lipids as the brewer's yeasts. Among phospholipids phosphatidylethanolamine prevailed in all strains tested. The phosphatidylcho‐line content was almost ten times higher in brewer's yeasts whereas the amounts of phosphatidylserine and phosphatidylinosi‐tol were two to three times higher in baker's yeast strains. The ratio of saturated to unsaturated fatty acids was always lower with brewer's yeasts. The differences in fatty acid composition were less pronounced than the differences in phospholipid composition.