Conditions have first been developed for the preparation of erythrocyte immunoglobulin diagnostic preparation of erythrocyte immunoglobulin diagnostic preparation for HFRS virus which permits express detection of the specific virus antigen in suspensions of the lung tissue of rodents by means of the indirect hemagglutination test (IHA) and laboratory diagnosis of the infection in humans by means of antibody detection by the indirect hemagglutination-inhibition test (IHAI). The IHA test is as sensitive as immunofluorescence, while the sensitivity of the IHAI test is not inferior to that of immunofluorescence but is higher than that of RIA.