Abstract. Results of current study have shown that acute brucellosis is characterized by increase of T-helper and cytotoxic T-lymphocytes and decrease of phagocytic activity of neutrophyls in the blood. In patients with chronic form of disease the decline of T-helper and cytotoxic T-lymphocytes together with activation of humoral immunity and increasing of B-lymphocytes and levels of immunoglobulins A and G have been observed. Thus, revealed changes indicating the formation of secondary immunodeficiency in chronic disease course. Results of the study confirmed the needs for a permanent immunological monitoring of patients with brucellosis as well as conducting a comprehensive immunological testing of patients to develop the individual scheme of corrective therapy.