Background : The main function of melanocyte is known to proiect the skin from hazardous sun-light. But, some investigators have claimed lately that melanocytes are also related to the immunologic role in the epidermis becauase these cells produce IL-1 activity and IL-lb convertase activity, in vitro. Objective : Our purposee were to investigate the effects of rIFN-b on the proliferation of melanocytes, melanin content, and the expression of HLA-DR aritign on melanocytes after a rIFN-y exposure. Methods : The number of melanocytes, the melanin content, and the expression of HLA-DR antigen were evaluated on culturect human melanocytes according to a time sequence and various concentrations of rIFN-y. Results : Antiproliferative activity on melanocytes was dependent on the exposure time and the concentration of rIFN-r. According to the exposure time and the concentration of rIFN-r, melanogenic activity was inhibited or stimulated, Normal melanocytes didnt express HLA-DR antigen, but when normal melanocytes were exposed to rIFN-r, the expression of HLA-DR antigen increased in a timeand concentration-dependent fashion. After the removal of rIFN-r fiom the culture media the expression of HLA-DR antigen on melanocytes also disappeared. Conclusion : In our study, melanocytes seem to be related to the irnmunologic role in the epidermis because these cells expressed HLA-DR antigen after rIFN-r exposue and we think that study could help to investigate between melanocytes and immunalogic mechanisms in various inflammatory skin diseases. (Kor J Dermatol 1993; 31(1): 359-369)