Although there have appeared in the literature several studies on the lipids of Tetrahymena, these reports are few indeed as compared with those dealing with the more general biochemical aspects of this important animal microorganism (see CORLISS (1954) for a review). MCKEE, DUTCHER, GROUPE and MOORE (1947) reported on the antibacterial action of lipids from Tetrahymena pyriformis W . KIDDER, DEWEY and HEINRICH (1954) showed that proteose-peptone grown Tetrahymena contain over 17% lipid material, which is in good agreement with the figure given by MCKEE et al. (1947), while Tween grown organisms contain over 44% lipid material. MUL-LER, FARKAS and HEKODEK (1959) investigated the fatty acid composition of Tetrahymena pyriformis GL. They found a highly complicated fatty acid pattern containing fatty acids with unusually long chains. These few papers have served to emphasize the need for the further study of this class of compounds, as no thorough and systematic fractionation of these materials from the organism has been made up to date. I n the present investigation, lipids were extracted from Tetrahymena with chloroform-methanol and washed with distilled water. The total lipid extract thus obtained was employed for estimation of lipid-phosphorus, solvent-fractionation and partial identification by means of column and paper chromatography.