A series of hybridomas producing monoclonal antibodies (McAb), specifically interacting with Herpes simplex virus (HSV) proteins, types 1 and 2, has been obtained. McAb 7c4 and 4f6 have been shown to be highly active in the solid-phase enzyme immunoassay (EIA) and to produce no reaction with HSV antigen in the indirect immunofluorescent assay (IIFA). McAb 2b6, 3e5, 4A, 2C effectively detect McAb in IIFA, but not EIA, while McAb 3d 10 exhibit activity in both biochemical assays. Moreover, as established in this investigation, McAb 4A are active against the protein of HSV capsid, McAb 3d10 and 2b6 detect two individual epitopes on the molecule of ribonucleohydreductase, McAb 2C are specific with respect to surface glycoprotein gB, McAb 7c4 and 416 recognize one or two overlapping epitopes of protein gD. McAb 2C are capable of completely neutralizing the infectious activity of HSV in the in vitro cell system. As determined by IIFA, McAb 4A and 4e5 stain specific inclusions in the nucleus of HSV-infected cells, while McAb 2C stain HSV protein, localized in the cytoplasm. All above-mentioned McAb are active against two common antigenic determinants of HSV 1 and HSV 2. The data obtained in this investigation suggest that the series of McAb under study may serve as the basis for the development of diagnostic test systems for the detection of HSV, types 1 and 2, by EIA and IIFA techniques.