Thirty-eight infertile women, possessing sperm-immobilizing antibody (SIA), were examined for their HLA-DR and -DQ types using DNA obtained from peripheral blood cells. The typing of HLA-DR and DQ was performed by polymerase chain reaction sequence specific oligonucleotide probes (PCR-SSOP) and PCR-restriction fragment length polymorphism (RFLP), respectively. In comparison to the normal Japanese population, the SIA positive patient population had higher genes frequencies in HLA-DRB1*0901 (26.3 vs. 13.6%, P<0.005), DQB1*0602 (13.2 vs. 6.2%, P<0.05) and -DQB1*0303 (26.3 vs. 14.8%, P<0.01), but not in any HLA-DQA1 gene types by chi2 test. After Bonferroni correction, the high frequency of HLA-DRB1*0901 remained significant (P<0.05) and HLA-DQB1*303 was slightly significant (P<0.07) but no other genes had a gene frequency significantly higher than that of the normal Japanese population. HLA-DRB1*0901 and HLA-DQB1*0303 are very rare among Caucasians but characteristically high among Japanese. The high frequency of HLA-DRB1*0901 and DQB1*0303 genes in the Japanese population may account for higher frequency of sperm-immobilizing antibody in Japanese compared to other ethnic groups.