Seven neutralizing monoclonal antibodies (MAbs) to the rotavirus simian agent 11 were produced. Although displaying variable degrees of haemagglutination-inhibiting activity, they were shown by radioimmunoprecipitation and Western blot analyses to react with the major outer capsid glycoprotein (VP7). In competition binding assays, MAbs defined two distinct VP7 epitopes, which appeared to be close to each other or partially overlapping. In addition, MAbs of the two epitope groups enhanced binding of a broadly reactive, non-neutralizing, MAb specific for rotavirus group antigen.