31 Palyam serogroup viruses were examined by complement-fixation and plaque-reduction neutralization tests and by PAGE of the segmented, double-stranded (ds) RNA genome. Although the viruses were indistinguishable by complement-fixation tests, 10 distinct virus serotypes were identified by plaque-reduction neutralization methods. Palyam group viruses which were distinct by the neutralization test had unique dsRNA profiles, whereas those agents which were indistinct by the neutralization test had identical dsRNA profiles. 20 isolations of 3 Palyam serotypes were made from bovines and Culicoides midges in Australia over a 9-year period. When the genome of these isolates was examined electrophoretically, the dsRNA profiles of virus isolates within a given serotype were identical.