Four isolates of soybean mosaic virus (SMV) from soybeans in Thailand were identified by host range, serology, transmission and electron microscopy. The host range of the four isolates differed in reactions in a few plants. Isolates of SMV from Thailand could be classified into two serological groups which were different from a SMV isolate from Japan. Two isolates of bean common mosaic virus (BCMV) from mungbeans in Thailand were transmitted by aphids and through mungbean seeds. The plants which showed systemic symptoms by mechanical inoculation of the isolates were limited to Leguminosae. Isolates of BCMV from Thailand consisted of flexuous filaments about 750 nm in length, which reacted strongly with antiserum to BCMV isolated from bean in Japan. A seed-borne, aphid-transmitted virus isolated from infected asparagus bean in Thailand had a relatively wide host range. The virus consisted of flexuous filaments about 750 nm in length, which reacted strongly with antiserum to the Florida isolate of blackeye cowpea mosaic virus (BICMV). Based on these results the virus was identified as BlCMV. In double-diffusion test in agar gel containing 0.5% lithium 3,5-diiodosalicylate, BCMV and BlCMV were serologically identical, and SMV was serologically related to, but distinct from BCMV and BlCMV.