A virus, designated as beet necrotic yellow vein virus (BNYVV), was isolated from sugar beet plants affected with rizomania disease. The virus was transmitted through the soil and by sap inoculation, but not by the aphids, Myzus persicae and Aulacorthum solani. Of 84 species of plants belonging to 16 families inoculated by sap, 15 of 17 species belonging to Chenopodiaceae, Tetragonia expansa and Gomphrena glohosa plants became infected with the virus. The virus tended to be restricted to the inoculated leaves of all host plants, but sugar beet, spinach, and Beta macrocarpa plants occasionally became infected systemically. The thermal inactivation point of the virus was between 65 and 70C, the dilution end point was 10^-4, and the infectivity was retained for 5 days at 20C or for 8 days at 4C. BNYVV particles (isolate YS) had a diameter of about 20nm and three peaks of length distribution at 95-110nm, 255-270nm, and 370-390nm. The virus was partially purified by organic-solvent clarification and polyethylene glycol precipitation. An antiserum to BNYVV had a titer of 1/1, 024 in ring precipitin tests. In agar gel-diffusion tests, a band of precipitation was produced between the virus and its antiserum. BNYVV did not serologically relate to soil-borne wheat mosaic virus, tobacco rattle virus, and tobacco mosaic virus. The present cryptogram of BNYVV is ^*/^*:^*/^*:E/E:S/(Fu).