The lipid class composition of beef heart ventricle was determined by a combination of diethylaminoethyl cellulose column chromatography and quantitative thin-layer chromatography. Percentages of the total lipid were: triglyceride, 43.6; cholesterol, 7.4; phosphatidyl choline, 22.8; phingomyelin, 4.0; phosphatidyl ethanolamine, 11.2; diphosphatidyl glycerol, 5.8; phosphatidyl serine, 1.2; phosphatidyl inositol, 3.0; phosphatidyl glycerol, 0.9; unsaturated hydrocarbon, 0.02; saturated hydrocarbon, 0.20. Nonlipid components represented 33.6% of the crude chloroform/methanol extracts.