Sphingolipids are derivatives of the long-chain amino alcohols sphingosine and dihydrosphingosine. The sphingoid long-chain base is linked to a fatty acid molecule via an amide bond-forming ceramide. The addition of carbohydrates to this ceramide backbone leads to the formation of a great diversity of glycosphingolipids, including the gangliosides GM1 and GM3 that differ only in their oligosaccharide chains. Like cholesterol, sphingolipids are found to be enriched in membrane rafts; this behavior is due to the presence of two long saturated alkyl chains that can be organized and condensed by sterols to form the liquid-ordered phase of membrane rafts [49] . In sperm, other investigations on nonprotein raft markers have focused on GM1. Using cholera toxin, this ganglioside was shown to localize to the plasma membrane overlaying the acrosome in living sperm [32] . On the other hand, using biochemical methods, it has been demonstrated by biochemical methods that GM3 is the most abundant ganglioside in the male reproductive tract and in sperm [39] [40] [41] ; however, localization of GM3 in these cells was undetermined. In this study, we used previously validated antibodies against GM3 [42, 43] to determine the immunofluorescence pattern of this ganglioside in sperm and found it to be restricted to the equatorial segment.