Lipid rafts are ordered membrane microdomains e n r i c h e d i n c h o l e s t e r o l , g l y c o l i p i d s a n d s a t u r a t e d phospholipids. Lipid rafts also assemble molecules involved in cell adhesion and signaling, and they are thus considered platforms for these phenomena. This has made the lipid raft topic a very active research field. However, a number of issues remain controversial in this research line. Advanced imaging studies have recently indicated that individual lipid/membrane rafts are of nanometer sizes. This suggests that rafts isolated from cells as low-density membrane fractions may rather represent "macrorafts" due to coalescence of individual rafts. Further controversy lies in the use of Triton X-100 in raft isolation, as the detergent may induce lipid microdomain formation. Investigators in the field are moving towards using milder non-ionic detergents or physical forces in raft isolation. Sperm-egg interaction is an ideal system to attest the implication of lipid rafts in cell adhesion/signaling. Recently, we have shown that Triton X-100 resistant membrane rafts of capacitated pig sperm have direct binding to pig zona pellucida (ZP) with a K d value much lower than that of noncapacitated sperm rafts-ZP binding. These results may partially explain the enhanced ZP binding ability of capacitated sperm, relative to non-capacitated sperm. Another possible contribution to the greater ZP binding ability of capacitated sperm is their possession of higher lipid raft levels despite a cholesterol efflux occurring during capacitation. Significantly, GM1 ganglioside, normally used as a raft marker of somatic cells, does not exist in capacitated sperm rafts. Rather, 70% of male germ cell specific sulfogalacotosylglycerolipid (SGG) is present in isolated capacitated sperm rafts, making it an attractive candidate as a sperm raft marker. Nonetheless, since sperm lipid rafts used in these studies were isolated by the Triton X-100 treatment method, work should be repeated using lipid rafts prepared from sperm by a physical force (e.g., nitrogen cavitation). Finally, advanced imaging studies