Metabolism and function of mouse phagocytes were studied experimentally under conditions of immunosuppression with biologically active substances. It was shown by the cytochemical methods with the use of cytophotometry that strong immunosuppression with azathioprin, prednisolone, especially with their combination induced inhibition of the enzymatic systems responsible for synthetic and energy processes in macrophages. Prodigiosan, a bacterial lipopolysaccharide, and lysozyme promoted elimination of the unfavourable effect of the immunosuppressors on macrophage metabolism, normalizing the decreased activity of certain enzymes and markedly activating the enzymes involved in detoxification and phagocytosis. The lysozyme effect did not depend on the type of drug immunosuppression. The efficiency of prodigiosan was the highest after administration of prednisolone or its combination with azathioprin. Its effect was lower after immunosuppression with azathioprin alone. During allotransplantation, prodigiosan also promoted the recovery of the leukocyte adsorption and digestive capacity impaired by prednisolone and tis combination with azathioprin. The differential use of the biologically active substances is a promising trend in control of complications due to immunosuppression therapy.