Wuhutang, a well known traditional Chinese. herbal decoction for the treatment of as thma was found to havc an antiviral effect on respiratory syncytial virus (RSV ) both invitro and in vivo. A 50% reduction of plaque. formation was observed op Hep-2 cell monolayer at a concentration of 1:80. At such concentration, the. value of lg TC ID50 of. Viralyield was 2, 1, and 55% RNA synthesis of RSV was inhibited. It was found that among thefive medicinal herbs in prescription Ephedra sinica Stapf is responsible for the antiviralactivity on RSV. IC50 for plaque inhibition was found to be 1.6mg/ml. In animal model,Wuhutang singn ficantly reduced the titre of RSV and accelerated RSV clearance in mice,and alleviated viral pneumonitis by either oral or aerosol route.