The physico-chemical structure of African horsesickness virus (AHSV) is compared with that of some of the other members of the Reoviridae, and in particular with that of bluetongue virus (BTV), the type strain of the orbivirus genus. This study adduces evidence of a great similarity between the gel electrophoretic patterns of the polypeptides of AHSV and BTV. The molecular mass values of the 7 AHSV polypeptides range between 0,30 x 10(5) and 1,46 x 10(5) dalton, a variation similar to that of BTV. The close relation between AHSV and BTV is further affirmed by the gel electrophoretic resolution of the AHSV double-stranded RNA genome into 10 segments.