BACKGROUND Phagocytes (polymorphonuclear cells and monocyte-macrophages) are the first line of defence of the host against infectious microorganisms and other foreign antigens. Agents which participate in activation of phagocytic cells possess a potential immunomodulating action. Thus, search for convenient in vitro test-systems and study of mechanisms of action of these agents are of practical interest. MATERIAL AND METHODS Human blood polymorphonuclear (PMN) cells and murine macrophages (line J774.2) were used as cellular test-systems for study of phagocytosis-stimulating action of immunomodulating agents. Indexes of phagocytic activity were estimated by the phagocyte ingestion of yeast cells. NO-synthase activity, nitrite production, and nitroblue tetrazolium test were determined after phagocyte stimulation. RESULTS It was revealed that indexes of phagocytic activity can be used as quantitative indicators for measurement immunomodulating activity. Zymosan A-induced phagocytosis in almost 100% PMN cells and macrophages and thus can be used as a positive control. Wheat germ agglutinin (WGA, 0.5-1.0 microg/ml) stimulated phagocytosis in PMN cells 1.8 times after 2-3 h incubation, although in higher concentrations (5-10 microg/ml) it strongly inhibited phagocytosis. TGF-b1 (10 ng/ml) suppressed phagocytosis in WGA-stimulated PMN cells. Mistletoe agglutinin-1 stimulated phagocytosis in PMN cells, although its effect in macrophages was weak, while concanavalin A stimulation of phagocytosis in macrophages was well expressed. Vasodilating peptide bradykinin increased phagocytosis 2.5 times in macrophages. We did not reveal changes in NO-synthase activity and nitrite production in macrophages and PMN cells activated by different immunomodulatig agents. Only lipopolysacharide stimulated such activity in macrophages. CONCLUSIONS Cultured macrophages and PMN cells can provide reproducible quantitative results in screening phagocytic activity of different immunomodulating agents. Both positively and negatively acting immunomodulators might be studied using these test cells.