In this paper the effect of Astragalusmembranaceus on the parainfluenza I（Sen-dai）virus infection in mice and its epide-miological efficacy in the prophylaxis ofcommon cold were described.Results of 28experiments carried out in mice under dif-ferent conditions demonstrated that Astraga-lus membranaceus was able to slightly pro-tect mice from lethal Sendai virus infection.The efficacy index averaged about 1.67.Theplacebo-controlled field studies on its ef-ficacy in the prophytlaxis of common coldwere carried out among 1827 volunteers in1974—1978.It was shown that the treatmentwith Astragalus membranaceus resulted notonly in decreasing the incidence of commoncold in 50%

but also in shortening thecourse of illness in patients suffering fromrecurrent common cold;the symptoms sho-wing deficiency of vital energy were marke-dly improved in 65.3% of patients within20 days after administration with Astragalusmembranaceus;the epidemiological efficacyof combined low titered interferon withAstragalus membranaceus for the preventionof common cold was more higher than thatof interferon alone.Results obtained maypartially explain why“Yu-Bing-Feng-San”is effective in the treatment of recurrentcommon cold

especially in cases of chronicbronchitis.