We previously identified a number of proteins using a combination of one-dimensional PAGE and tandem mass [20] . To confirm their association with the light-density fractions, antibodies against these proteins were obtained from different commercial and noncommercial sources as enumerated in Materials and Methods. Each of these antibodies was validated by Western blot of total sperm extracts as shown in Figure 1A , and the antibodies recognized proteins of the predicted molecular weight. In addition to the proteins identified previously [20] , we assayed for the presence of other proteins known to be enriched in membrane rafts in many cell types such as CAV2, FLOT1, and FLOT2. Antibodies against these proteins react with polypeptides of the expected molecular weight, indicating the presence of these proteins in mouse sperm (Fig. 1B) . We also tested antibodies against ADCY10, a nonraft protein.