Sixty six infertile men with cytotoxic sperm antibodies had fewer and lower percentages of OKT4–positive helper/inducer T lymphocytesp= 0.004 and 0.003, respectively), than the fertile (n= 14) and infertile (n= 12) antibody-negative controls. Ratio of OKT4/OKT8 was decreased (p<0.01). while numbers of OKDR and BD-Leu 12 positive predominantly B lymphocytes were increased (p<0.000l) in infertile men with sperm antibodies. T lymphocytes positive for OKT3, OKT11 and OKT4 and the OKT4/OKT8 ratio were decreased in infertile women with sperm antibodies, while B lymphocytes positive for OKDR and BD-Leu12 were increased in infertile women with or without sperm antibodies (p<0.0001, versus fertile controls). Lymphocyte responses to phytohemagglutinin (PHA), concanavalin A (ConA) and pokeweed mitogen (PWM), however, were similar in 20 fertile and 136 infertile couples. Lymphocytes from infertile men with sperm antibodies had an enhanced stimulatory response to autologous sperm and seminal plasma. It is concluded that sperm antigens from autoimmune infertile men stimulate heightened immune responses to sperm antigens and altered distribution of white cell populations in both partners.