Neutralizing monoclonal antibodies (mAbs) have been produced and used to map the topographical relationship of the surface antigenic determinants of bluetongue virus (BTV) 17 that mediate neutralization. Eight monoclonal antibodies, at least five of which were directed to the major outer coat protein of BTV 17, P2, were studied in neutralization assays using variant BTV 17 and in competition binding experiments. Five different epitopes were identified that are involved in neutralization of viral infectivity. Three of the five epitopes are clearly associated with P2, while the location of the other two epitopes is not known. The potential association of these two epitopes with one or both outer coat proteins of BTV is discussed.