Two hundred forty-two cases of subzonal insemination (SUZI) were performed in 172 infertile male patients. Criteria for selection of subjects to receive SUZI were as follows; those who had previously failed to achieve fertilization by conventional in vitro fertilization (IVF) with normal semen analyses (group 1, n = 36), those who had previous fertilization failure in conventional IVF with abnormal semen analyses (group 2, n = 49) and those who had not been accepted for IVF because of severely abnormal semen analyses (group 3, n = 87). Two to twenty spermatozoa were injected into the perivitelline space of metaphase II oocytes. Fertilization occurred in 77.3% of patients and 40.9% of 1,220 eggs and 28 clinical pregnancies were established. There were no significant differences in fertilization rates, cleavage rates and embryo transfer rates among the three groups. However, the pregnancy rate was significantly lower in group 1 (7.7%) than in group 2 (20.0%) and group 3 (14.5%) (p < 0.05). These results indicated that SUZI improved the incidence of fertilization in male infertility. However, the fact that the lowest pregnancy rate was in group 1 indicates that further studies of patients with idiopathic failure of fertilization are needed.