Immunofluorescent localization of RNase 9 on non-capacitated and capacitated human spermatozoa. Smears of non-capacitated (A–D) and capacitated (E–H) human spermatozoa were probed with Fab of mouse anti-RNase 9 antiserum (A, B, E, F), mouse anti-RNase 9 antiserum that had been preabsorbed with recombinant RNase 9 from E. coli (C, D, G, H). The fluorescent images are shown in A, C, E and G and the corresponding phase-contrast images are shown in B, D, F and H. Micrographs are representatives of spermatozoa observed from five different males. Original magnification × 1 000. Bars = 500 μm.