Background and Aim:  The factors that affect sperm immobilizing antibody production in some women are not fully understood. This study was performed to investigate if production of sperm immobilizing antibodies in women is associated with their husbands' sperm count. Methods:  The sperm immobilization test (SIT) was performed on 221 infertile women whose husbands had normal semen characteristics according to the criteria by WHO; 160 patients were treated by intracytoplasmic sperm injection (ICSI) because of poor semen characteristics, and 1013 virgin female children acted as the controls. Results:  A significant difference of the incidence in SIT was observed between the virgin female children and the women whose husbands had a normal sperm count (P < 0.0001). There was also a significant difference of the incidence in SIT between the women treated by intracytoplasmic sperm injection (ICSI) because of a severe male factor and those whose husbands had a normal sperm count (P < 0.05). Conclusions:  These results indicate that production of sperm immobilizing antibodies in women begins after they have been exposed to a large enough amount of sperm. However, the precise amount of sperm required to produce the antibodies is not clarified by the present study. (Reprod Med Biol 2003; 2: 105-108).