SUMMARYHybridomas were developed that secreted antibodies to soybean mosaic (SMV), lettuce mosaic (LMV) viruses, and to maize dwarf mosaic (MDMV) virus, strains Ap and B. All hybridomas produced antibodies specific to the homologous virus except for one to LMV, which produced antibodies that reacted at a low level with SMV and MDMV. Monoclonal antibodies against SMV were used in a double-antibody sandwich radioimmunoassay. The assay using only one type of monoclonal antibody lacked sensitivity because, presumably, limited epitopes were available. Results obtained using two monoclonal antibodies that bound to different epitopes were comparable to those using polyclonal antibodies. A competitive radioimmunoassay, using a single monoclonal antibody, was developed to detect successfully SMV, LMV and MDMV.