The interactions of xenobiotics with the immune system can finally induce immunosuppression or immunopotentiation. It is of great importance to study the early detection of immune deficiencies and modifications of the non-specific defence mechanisms. The immunostimulants are the agents that stimulate the response of effector cells such as macrophages, neutrophils and lymphocytes. They are not specific for a particular antigen, and are capable of enhancing non-antigen-specific resistance against infectious or neoplastic conditions. The purpose of this study was to determine the possibility of modulating the cellular immune response with the dimer of lysozyme (KLP–602) in rabbit after suppression induced by atrazine. Dimerized lysozyme is a natural immunomodulator obtained by monomer dimerization. It is an active substance of the preparation Lydium KLP, which is introduced to veterinary treatment in Poland. In the in vivo study rabbits were given an intraperitoneal injection of atrazine at the dose of ¼LD₅₀, then after 48 h they were administered the dimer of lysozyme (KLP–602) at the dose of 0.02 mg/kg b.w. After 2, 4, 7, 14 days post intoxication cells from blood of rabbits were isolated. In the study we determined the metabolic activity of phagocytes and the proliferative ability of T and B lymphocytes. The results indicate that this modulator is useful for stimulation of cellular and humoral immunity after experimentally induced suppression by the selected pesticide.