85 hantavirus (HV) strains from Russia and other counties were examined by indirect fluorescent antibody test using monoclonal antibodies (MAbs) prepared against hantaviruses: Hantaan (Hantaan 76-118, A-9 strains), Seoul (SR-1, R-22 strains) and Puumala (Hallnas 83-223 strain). 68 HV strains were differentiated into five virus type groups: Hantaan, Puumala, Seoul, Prospect Hill and Belgrade-Dobrava. 17 strains were found to be antigenically closely related but distinct from Hantaan type (4 strains), Puumala (6 strains) and Prospect Hill (7 strains). The antigenic characteristics of these 17 strains suggested two supplementary antigenic subgroups of the Hantaan, two of Puumala and two of Prospect Hill.