Osthole which has been long used in China as a herbal medicine to improve male sexual dysfunction. Bioassay-directed fractionation led to the identification of four known coumarins osthole, imperatorin, xanthotoxin, and isopimpinellin from the ethanolic extract of the fruits of Cnidium monnier (L) Cusson. Furthermore, we investigated the cavernosal relaxant effect of osthole. In the present study, corpus cavernosal strip showed relaxation in response to osthole (0.1-30 .mu.M) in a dose-dependent manner. Corporal relaxation elicited by osthole was reduced partially but significantly by pretreatment with L-NAME, ODQ and by endothelial disruption, however, were not affected by indomethacin and tetradotoxin treatment.