The prevalence of cytomegalovirus (CMV) infection and viral shedding in infertile couples in Taiwan and its role in infertility were studied. Two hundred fifty couples were enrolled in this study. Anti-CMV IgG was measured in serum samples from these infertile couples. Viral shedding examined by DNA hybridization was detected in semen from the husband and cervical mucus from the wife. Anti-CMV IgG was detected in 249 (99.6%) of the 250 male serum samples and in 247 (98.9%) of the 250 female serum samples. Viral shedding was detectable in 83 (33.5%) of 248 semen samples and 83 (33.7%) of 246 cervical mucus samples by dot-blot DNA hybridization assay. Semen quality was not apparently affected by the existence of viral shedding. The co-shedding rate in semen and cervical mucus was high (15.9%). It is concluded that the seroprevalence and genital tract viral shedding were relatively high in infertile couples in Taiwan. Viral shedding did not affect the semen quality. Nevertheless, screening of donor semen is recommended.