Rapid staining for the sperm penetration assay using a bisbenzimide dye

Our rapid staining method, accomplished by adding the vital fluorochrome bisbenzimide (Hoechst 33342) directly into the sperm droplet before fertilization, eases visual interpretation of sperm penetration and decondensation. For both within- and between-experiment comparisons, inclusion of bisbenzimide did not influence the overall SPA score or the progress of sperm-egg interaction. These results suggest that bisbenzimide can be used routinely to facilitate scoring of the SPA.