Abstract Purified bluetongue virus was shown to possess a double-stranded RNA genome, very similar to that of reovirus, consisting of at least three double-stranded components. A low molecular weight component probably equivalent to the adenine-rich single strand found in reovirus was present in varying amounts. The two viruses differ, however, in stability and serological characteristics, reflecting profound differences in morphology. The classification of all double-stranded RNA viruses in a new group is proposed.