The possibility for sphingomyelin and ceramide: phosphoethanolamine synthesis in ram spermatozoa plasma membranes has been established. 2. Ceramide: phosphoethanolamine formation appears to be higher than the synthesis of sphingomyelin. 3. The pH optimum of the phosphatidylethanolamine: ceramide-phosphoethanolamine transferase is about 7.0. An inhibition of its activity was observed in the presence of Ca2+ and Zn2+ ions.