The molecular species compositions of phosphatidylcholine, -ethanolamine, -serine, and -inositol in microsomes and rod outer segments from bovine retina were studied by means of argentation thin-layer chromatography (TLC) after conversion of the phospholipids to labeled acetyldiacylglycerols. A highly unsaturated group of molecular species, called "supraenes" to indicate the presence of more than six double bonds per molecule, was present in all four glycerophospholipids. Docosahexaenoic acid was the major component of these species, in combination with other unsaturated fatty acids, predominantly polyunsaturates. The presence of species containing docosahexaenoate in both positions of the glycerol backbone was suggested by the high percentage (95%) of these fatty acids in the most polar fraction of phosphatidylcholine. In rod outer segments, supraenes were the major component of phosphatidylserine (51% of the molecular species), followed by phosphatidylcholine (31%), phosphatidylethanolamine (21%), and phosphatidylinositol (9%). Hexaenes, which contained docosahexaenoate and saturated fatty acids, predominated in phosphatidylethanolamine (67%), followed by phosphatidylserine and phosphatidylcholine (about 36%), and phosphatidylinositol (12%). Tetraenes made up half the phosphatidylinositols, but amounted to less than 5% of the other glycerophospholipids. Disaturated and monoenoic species made up 14 and 6%, respectively, of phosphatidylcholine. In microsomes, there was less of the docosahexaenoate-containing species and more of the saturated to tetraenoic species. Monoenes predominated in phosphatidylcholine (35%), tetraenes in phosphatidylinositol (71%), and hexaenes in phosphatidylethanolamine and phosphatidylserine (50 and 42%). Supraenes amounted to less than 15% of each of the four glycerophospholipids in microsomes.-Aveldaño, M. I., and N. G. Bazán. Molecular species of phosphatidylcholine, -ethanolamine, -serine, and -inositol in microsomal and photoreceptor membranes of bovine retina.