Garlic components are known to modulate certain immune functions. However, mechanisms of their action are not sufficiently elucidated. This study was, therefore, undertaken to examine the effects of aqueous and ethanolic extracts prepared from a garlic powder sample on proliferation of rat spleen Iymphocytes in culture. Cells were stimulated with the combination of phorbol myristate acetate (PMA) and a Ca ionophore (A23187) or R73 monoclonal antibody (mAb) directed to the α β chain of T cell receptor. It has been shown that both extracts significantly stimulated proliferation of lymphocytes. The effect correlated with upregulation of the Interleukin 2 receptor a (IL-2Rα) expression and the increase in IL-2 production. Stimulation of IL-2 production by the extracts was higher in cultures with PMA / Ca ionophore than in cultures with R73 mAb. In contrast, both extracts stimulated production of IL-4 by splenocytes triggered by R73 mAb. The complete dependence of lymphocyte proliferation in cultures with R73 mAb and garlic extracts on IL-2 and IL-4 was demonstrated using neutralising mAbs to IL-2Rα and IL-4. These results suggest that the potentiating effect of garlic extracts on lymphocyte proliferation in vitro differs depending on specific stimulators of cell proliferation and probably on the type of responding cells.