Thirty five couples were treated by intrauterine insemination with sperm prepared by a washing and swim-up method. Fifteen women conceived(42.9%). Sperm washing and swim-up was found to significantly improve sperm motility for men of infertile couples and the increment of percent sperm motility after sperm preparation allowed significant differentiation of pregnant and nonpregnant patients in asthenozoospermia(submotile) group (p<0.01). The author suggest that the increment of percent sperm motility after sperm washing and swim-up could be a useful screening tool for in vitro procedure proposed to improve fertility in the intrauterine insemination of asthenozoospermia.