Phosphatidylcholine, phosphatidylethanolamine and triacylglycerol were isolated from egg yolk of the Japanese quail. Fatty acid compositions at the two and three positions of glycerol in the glycerolipids were determined by stereospecific analysis employing phospholipase A2. The distribution of the total number of carbon atoms in the fatty acid moieties of triacylglycerol was also quantitated by high temperature gas liquid chromatography. The distribution of acyl groups in each of the positions of the phosphatidylcholine, phosphatidylethanolamine and triacylglycerol was not random, and each position has a characteristic composition. The phosphatidylcholine and phosphatidylethanolamine had distinctive fatty acid distributions for position sn-2 of the triacylglycerol had a predominance of unsaturated fatty acids of which 18:1 (69.9%) was the major component. Position sn-3 contained 49.3% saturated fatty acids and was more saturated than position sn-1 by 8.1%. The experimentally determined distribution of the carbon numbers in triacyl glycerol deviated significantly from the distribution predicted by 1-random-2-random-3-random association of the fatty acids. The data suggest that in Japanese quail there is marked preferencial synthesis of some triacylglycerols.