A hybridoma panel producing monoclonal antibodies to immunochemically non-identical antigenic epitopes of the protein nature located in outer membrane of Yersinia pseudotuberculosis was obtained. It was revealed that the previously identified B-antigen protecting laboratory animals from experimental plague was detected using both monoclonal antibodies against mentioned protein determinants and the determinants of lipopolysaccharide O-side chains. The B-antigen is a component of the Y. pseudotuberculosis outer membrane, egested in the form of the vesicles (OMVs) by bacteria cultivated in fluid nutrient medium.