Studies with the Tobacco Mosaic Viruses; W. S Kim, and So, I Y., (Dept. of biology Sung Kyun Kwan Univer. Seoul, Korea.). Using the common strain of tobacco mosaic virus (TMV) which was sent from the Dept. of Plant Pathology, University of Wisconsin, U.S.A. as control virus, a possible new strain of tobacco mosaic virus (SMV) was isolated from tobacco leaves collected from Tobacco Experiment Station farms as well as from various blends of manufactured Korean cigaretts. SMV was isolated by single lesion isolation method and by inoculating the virus through various species of host plants. The two viruses, TMV and SMV were indentified by the difference in symptoms, host range, serological reaction, and electron micrograpy. As the results of the above experiment the author believes the virus isolate SMV is a different strain of TMV. The experimental evidences that SMV belongs to the TMV group are as follows; 1. Both viruses produced local necrotic lesions on Nicotiana glutimosa L. 2. Both showed a dilution end point of $10^8$. 3. Aphid transmission was failed with the viruses. 4. Both had an isoelectric point around pH 3.3. 5. Two viruses were serological reactive. 6. The size of the virus particles was around 270-300mu as they were observed under the electron microscope. The virus SMV, however, is different from the common strain of TMV and the experimental evidences are as follows; 1. SMV produced quite different symptoms from TMV on various host plants like tobacoo(Nicotiana tabacum L., White Burley), Nicotiana rustica L., Chenopodium Koreanse Nakai. Bata vulgaris L., and Datura tatula L., SMV produced distinct local lesions on these host plants whereas TMV incited largely mosaic diseases. 2. The serological titers obtained from the heterologous combinations were lower than those from homologous combinations of antigens and antiser.