Twelve hybridomas secreting monoclonal antibodies (MAbs) against Miller virulent strain of transmissible gastroenteritis virus (TGEV) were generated and characterized. In a cell culture immunofluorescence (CCIF) assay, three MAbs directed against peplomer protein (E2) had perinuclear fluorescence and four unclassified MAbs showed cell membrane fluorescence. Six of these seven MAbs neutralized both attenuated and virulent TGEV, and the seventh (an unclassified MAb) neutralized only the latter virus. Two MAbs able to bind the cell membrane of infected cells had low neutralizing antibody titers (8 to 72) but were able to distinguish between virulent and attenuated TGEV (9- to 72-fold differences in neutralizing titers). Two E2-specific MAbs had higher neutralizing antibody titers (782 to 34,117) and showed 4- to 13-fold differences in titers against the attenuated and virulent TGEV strains. Five MAbs which were specific for nucleocapsid (N) protein had cytoplasmic, particulate fluorescence in CCIF, and did not neutralize TGEV. Comparison of CCIF antibody titers of MAbs to the virulent and attenuated strains of TGEV indicated that differences existed in titers of most E2 and all N-specific MAbs, with titers consistently higher against virulent TGEV (homologous strain). Hyperimmune antisera prepared in gnotobiotic pigs against the attenuated, virulent and a recent isolate of TGEV immunoprecipitated the 3 major structural proteins of both the attenuated and virulent TGEV strains. Relative mol. wt. differences in the E1 and E2 proteins between the two virus strains were revealed using either the hyperimmune pig sera or MAbs. In addition to the 48 K N protein, a 44 K protein was coimmunoprecipitated by the hyperimmune sera and MAbs, but mainly from lysates of attenuated TGEV.