Localization of PS on human spermatozoa. PS are visualized by labeling spermatozoa with annexin V-FITC staining. (A) A spermatozoa as seen under bright field microscopy. (B-F) Representative patterns of annexin V-FITC binding sites: head (B), midpiece (C), head plus midpiece (D), tail (E), or entire spermatozoon (F) plasma membrane as seen under fluorescence microscopy. Magnification ×900.