To clarify further the role of antisperm antibodies in in vitro fertilization, the occurrence of antisperm antibodies on ejaculated sperm and in sera was determined by the immunobead binding assay in 67 couples after an unsuccessful in vitro fertilization cycle. Antisperm antibodies in maternal sera were associated with a failure of oocyte fertilization (P less than 0.02) or with fertilization of only 9-19% of the oocytes (P less than 0.01) in vitro. Antisperm antibodies were detected in sera from 13 of 24 women (54.2%) where no fertilization occurred, 9 of 14 women (64.3%) where less than 20% of the oocytes fertilized, and 3 of 19 women (15.8%) where greater than 40% of the oocytes fertilized. Antisperm antibodies in these sera were mostly IgG and directed against the sperm tail. Antibodies on the surface of ejaculated motile sperm were also associated with a low (9-19%) fertilization rate (P less than 0.01). Sperm-bound antibodies were detected in 2 of 24 men (8.3%) where no fertilization occurred, 5 of 14 men (35.7%) where less than 20% of the oocytes fertilized, and 0 of 19 men where fertilization was greater than 40%. Sperm-bound antibodies were mainly IgA and were tail-directed. Antisperm antibodies in sera of males were not related to the rate of fertilization.(ABSTRACT TRUNCATED AT 250 WORDS)