From September 1988 to August 1992, two different methods of preparing human sperm before intrauterine insemination(IUI) were compared using the semen samples of seventy-three infertile couples. The sperms were prepared by a swim-up after sperm washing or by a continuous percoll gradient technique. Fourteen of 35 women conceived during IUI cycles using a sperm washing and swim-up method (40%), and 12 of 38 women conceived during IUI cycles using a percoll gradient technique(31.6%). Among the group with male infertile etiologic factor only, one of 5 women conceived during sperm washing and swim-up cycles(20%); one of 4 women conceived during percoll gradient cycles(25%). On the contrary, among the group with cervical factor only, six of 10 women conceived during sperm washing and swim-up cycles (60%) ; Five of 17 women conceived during percoll gradient cycles(29.4%). It is suggested that sperm separation by sperm washing ar -up is a useful technique for intrauterine insemination in cervical infertility, and sperm separation in percoll gradient appears to be more valuable for intrauterine insemination of male subfertility.