Cavity problems which can develop after an open cavity mastoidectomy have received much attention in the field of otology. Recently, the incidence of chronic otitis media has decreased due to better economic and health condition, and as a result, cases of middle ear surgery have also relatively decreased in number. Therefore, otologists should now engage themselves more in searching for a treatment for these cavity problems. One of the cavity problems is that squamous debris accumulates in the ear canal which occasionally causes some trouble. Lately, histologic examination of this newly formed skin in the open-mastoidectomized cavity(cavity skin) was reported using a light and electron microscopic investigation (Park et al, 1989). However, further investigation about morphology of the cavity skin was needed to compare with that of cholesteatoma matrix. Thus, the aim of this study was to quantitate Langerhans' cells in the cavity skin using the immunohistochemical technique and to compare them with those in the cholesteatoma matrix and postauricular skin. The results obtained were as follows : 1) The Langerhans' cells in the cavity skin increased significantly, compared with those in the cholesteatoma matrix(<0.05) and postauricular skin (p<0.05). 2) The Langerhans' cells in the cavity and cholesteatoma matrix had more numerous and longer dendritic processes than those in the postauricular skin. 3) The more inflammation was in the subepithelial connective tissue, the more Langerhans' cell in the cavity skin increased in number.