A rod-shaped virus was isolated from naturally infected soybean (Glycine max (L.)Merr.) plants collected at Phitsanulok, northern Thailand, in 1979. The virus caused mild mottle symptoms in soybean and was transmitted by whiteflies (Bemisia tabaciGenn.), by sap inoculation, and through soybean seed, but not by the aphids, Aphis craccivora Koch and A. glycines Matsumura. Virus particles consisted of flexuous rods 10-15 x 650-700 nm in size. In tube precipitin tests, the virus reacted with antiserum to cowpea mild mottle virus (CMMV). Infectivity of the virus was retained in sap diluted to 10^-5 but not 10^-6, heated for 10 min at 70°C but not 75°C, or stored at 20°C for 21 days but not 28 days. The virus contained single stranded RNA and was identified as CMMV on the basis of host range, symptomatology, particle morphology, and serological relationships.