Abstract The time course of the loss of different components of the phospholipids of rabbit and mouse epididymal spermatozoa during spontaneous lipid peroxidation was determined, using thin layer chromatography with a specific situ hydrolysis method to differentiate the acyl and alkenyl (plasmalogen) moieties. The components followed were phosphatidylethanolamine (PE), phosphatidylcholine (PC), the PE and PC phasmalogens, sphingomyelin (SP), cardiolipin (CL), and phosphatidyl-glycerol (PG). In both mouse and rabbit sperm, the PE component was found to be more than 90% diplasmalogen: 1,2-di(0-1′-alkenyl) glycerophosphoethanolamine. This component was lost rapidly during peroxidation. All PE has disappeared from rabbit sperm after 4 h aerobic incubation, at which point the other phospholipids had been little affected. In both mouse and rabbit sperm, the PC component was found to be 50% monoplasmalogen. The decrease in PC plasmalogen of rabbit sperm amounted to 74% after 20 h, compared to 42% loss of total PC. Similar observations were made with mouse sperm, except that rates of loss of all components were approximately twice those in rabbit. Distribution of the phospholipid components between sperm heads and tails was also determined: PE diplasmalogen was almost entirely found in the tail fraction, in both mouse and rabbit sperm. This mode of analysis allows the differentiation of sensitivities towards spontaneous peroxidation of the different types of phospholipid present in sperm membranes.