Ultraviolet radiation of skin leads to a systemic alteratior tkat inhibits the normal pattern of immunologic tumor rejection., suppresses the contact hypersemisivity and transiently alters the morphology and the surface marker characteristics of Langerhans cells. Moreover, Ultraviolet radiation elaborates the ETAF, neuropeptides, proteins, and urocaicacid which may alter immunologic responses. But no other study about the effects of UVB irradiation on the systemic immunologic functions of the macrophages of internal organs was reported. The macrophages of the reticuloendothelial system (RES) play a central role in cell-mediated immunity, because they are involved both in the initiation of responses as antigen-presenting, cells, and in the effector phase as inflammatory, tumoricidal and microbicidal cells. The present study was intended to investigate the effects of UVB irradiation on the immunologic functions of mouse peritoneal macrophages. Normal 6-8-week-old BALB/c mice were exposed at the dose rate of 20mJ/cm and 40mJ/cm of UVB per day, 5 days per weeks for 2 weeks, 4 weeks and 8 weeks. Then the peritoneal macrophages were obtained from the mice and the changes of cell count, chemotactic index, phagocytic index, NBT reduction rate and superoxide (0) production were examined. The results were as follows : 1)the number of mouse peritoneal macrophages was decreased by UVB radiation, 2) the chemotactic index of mouse peritoneal macrophage was not altered by UVB radiation, 3) phagocytic activity of mouse pertoneal macrophage was significsntly decreased by UBV radiation, 4) NBT reduction rate in mouse aeritoneal macrophage after UVB radiation was sinificanily decreased in all experimental group, and 5) Superoxide (0) production in mouse peritoneal macrophage after UVB radiation was decreased in all experimental groups. (Kor J Dermstol 1993; 31 (1): 28-37)