The state of macrophage surface structures is closely connected with the function 1 capacity of these cells. Peritoneal macrophages from mice subjected to strong 10-day immunosuppression with azathioprine (60 mg/kg), prednisolone (50 mg/kg) or their combination (25 and 30 mg/kg, respectively) were investigated with scanning electron microscopy. Azathioprine and especially its combination with prednisolone induced pronounced degenerative affections in the macrophages and lymphocytes, smoothing of their surfaces, predominance of large spread macrophages, and impairment of the intracellular cooperation. The macrophage alteration under the action of prednisolone was less pronounced. Prodigiozan, a bacterial polysaccharide (0.5 mg/kg) administered on the 4th and 9th days of the immunosuppression increased the macrophage resistance mainly to the damaging effect of prednisolone and was low effective after administration of azathioprine. The effect of lysozyme injected intramuscularly in a dose of 0.5 mg/kg daily within a period of the 3rd to the 10th days of the use of the immunosuppressants was evident from activation of the surface structures of the small macrophages and lymphocytes and reduction of cell alterations independent of the type of the immunosuppressants used. This indicates the necessity of a differential approach to the use of the macrophage activators for correcting the decreased infection resistance after medicamentous immunosuppression.