During the period January 1, 1991 through December 31, 1995, 258 patients, in whom motile sperm counts for insemination (postwash, processed) were 10.0 million motile sperm or less were seen in the andrology unit for sperm washing and intrauterine insemination (IUI). No significant female factors were noted on history; all female partners had patent Fallopian tubes and were ovulatory spontaneously or were treated by the referring gynecologist with clomiphene citrate, human menopausal gonadotropin (hMG), or follicle-stimulating hormone (FSH) ovulation induction in both anovulatory or ovulatory women. Of the total of 258 patients, 15 achieved a pregnancy in 284 cycles of IUI in which the inseminating motile-count was < 1.0 million motile sperm, resulting in a monthly fecundity (f) of 5.3%. The mean (+/-SD) motile count for IUI in this group was 0.61 (+/-0.29) million sperm, with a range of 0.19-0.95 million motile sperm. The initial motile count was 2.97 (3.2) million sperm, with a range of 0.2-12.81 million sperm. With inseminating motile counts of 1.0-10.0 million motile sperm, there were 83 pregnancies after 467 cycles of IUI, resulting in a monthly f of 17.8%. The mean (+/-SD) motile count for IUI in this group was 4.9 (+/-2.7) million motile sperm with a range of 1.0-9.9 million motile sperm. The initial sperm count in this group was 10.9 million (+/-7.1), with a range of 1.1-23.7 million motile sperm. These data suggest that acceptable pregnancy rates can be achieved with IUI, even in severely oligozoospermic specimens. Intrauterine insemination is less invasive and less costly than other assisted reproductive techniques. These data are supportive of IUI prior to attempting other more invasive and potentially costly reproductive technologies.