To analyse the specific humoral immunity parameters in patients with hemorrhagic fever with renal syndrome (HFRS) during various periods depending on the severity of the disease, there has been carried out a clinico-immunological examination of 53 patients. It has been determined that in patients with HFRS the maximum values of specific Ig M were registered during the period of oliguria, and Ig G values during the period of early reconvalescence, the titres of total specific antibodies being in the inverse dependence on the severity of the disease. While evaluating the specific antibody total titre during various periods of the disease comparable in severity, the following results were obtained: all forms of HFRS revealed higher titres during the period of oligoanuria as compared to the period of polyuria. The revealed peculiarities may be attributed to the different character of class Ig M and Ig G antibody titres dynamics. Therefore, both the dynamics of specific Ig M and Ig G parameters in patients with HFRS a severe course of the disease and the total specific antibody dynamics during various periods of the disease, depending on its severity, follow the laws of humoral immunity reactions on the infection agent.