A survey of tabacco diseases in 25 counties,Hunan province over 1990~1991showed 7 types of symptoms in tabacco fields,out of which mosaic was the most prevalent.The results of differential host reaction examination and SPA-ELISA test of 62 and 162 sam-ples revealed respectively that the tabacco plants were infected by CMV,TMV,PVYandTRSV alone or combined and that CMV was the major one with 53.08% of infection fre-quency.SPA-ELISA test of 314 samples exhibiting mosaic symptom also indicated that thesamples w...