Intrauterine insemination with husband's sperm (IUI) is offered to couples with infertility due to various causes although there is no general agreement on which of these causes should be so treated. In this report 77 couples were diagnosed as having either cervical factor, male factor, immunological factor or unexplained infertility. Insemination was performed 24-32 hours after a rapid rise in the serum LH level. Two of 16 pregnancies which resulted miscarried, 1 was ectopic and the remainder were full term. Eleven occurred in the cervical factor group, 3 in the immunological factor and only 1 in each of the male factor and unexplained infertility groups. The differences in the number of pregnancies between the cervical factor and male and unexplained infertility groups are significant but not between the groups with cervical and immunological factors. The majority of pregnancies (81%) were achieved in the first 4 cycles. Patients with the cervical factor as the cause of their subfertility are likely to benefit from the IUI with their husband's sperm. The small number of patients with the immunological factor in this study does not allow for a conclusion. In our experience the male factor and unexplained infertility patients are unlikely to benefit from intrauterine insemination with husband's sperm.