Poor sperm motility is an important cause of male infertility. In an attempt to identify Chinese medicinal herbs that might improve human sperm motility in vitro, we screened water extracts of 18 herbs with a trans-membrane migration method which measured the percentage of sperm that moved across the 5 micron pores of a Nucleopore membrane from a semen-drug mixture into phosphate buffered saline during 2 hours incubation. Astragalus membranaceus was the only herb that showed a significant stimulatory effect. At 10 mg/ml, it increased the motility of sperm in semen to 146.6 +/- 22.6% of control. It also increased the motility of washed sperm to 138.2 +/- 13.8% of control. Purification of the active component(s) from this herb as well as its application in assisted reproduction technology await further investigation.