We performed intrauterine insemination with washed husband's spermatozoa in 27 couples with clear evidence of impaired sperm mucus interaction due to cervical hostility or immunologic male subfertility and in 30 couples with subnormal semen, but optimal cervical mucus qualities. In each couple insemination cycles were alternated with cycles during which normal intercourse took place. Both types of cycles were monitored for LH. When a clear rise of LH levels could be detected, either IUI was scheduled or intercourse advised for the following day. In the male subfertility group no difference between the pregnancy rates of insemination and intercourse cycles was present. In the group with impairment of sperm-mucus interaction, the pregnancy rate of the insemination cycles was 16%, whereas no pregnancies occurred during intercourse cycles.