This study documents the types and incidence of antisperm antibody, detectable by indirect immunofluorescence, in 114 patients before vasectomy, 112 at 2 months and 71 patients at 6-9 months after vasectomy. Indirect immunofluorescence techniques revealed antibodies to seven distinct sperm antigens. Five of these antigens were readily accessible to antibody in vitro, and the remaining two were accessible only after treatment of spermatozoa with dithiothreitol and trypsin. Antisperm antibodies were detected in 61% of patients before vasectomy. The incidence rose to 77% at 2 months and 90% at 6-9 months after vasectomy. These antibodies were distinguishable into two groups based on their incidence before vasectomy. The first group included antibodies to antigens in the acrosome with a diffuse distribution, the equatorial region, the postacrosomal region and the midpiece of the tail. Its incidence was 61% before vasectomy; increased to 73% at 2 months and 80% at 6-9 months after vasectomy. The second group included antibodies to the sperm nucleus, the tail and to discrete antigens over the acrosome. They were found rarely (3%) in patients before vasectomy; increased in incidence to 25% at 2 months and 55% at 6-9 months after vasectomy. Antisperm antibodies of both groups existed as IgG and IgM classes; an exception being antibodies to sperm nucleus which were almost exclusively IgG. Of the antibodies, 14% were found to fix complement in vitro. Other autoantibodies, including antinuclear, antimitochondrial and antismooth muscle antibodies, did not develop following vasectomy.