Melanocytes were identified by the dopa reaction, and counted in vertical sections of 183 specimens of normal skin and 218 specimens of patients with pigmentary disorders. The incidence of dopa-positive cells in the basal layer was determined. One cell in 9 in the basal layer was dopa-positive in normal specimens. There was no significant difference in the incidence of dopa-positive cells between male and female and between adult and children. Specimens from face, neck and prepuce revealed comparatively high incidence of dopa-positive cells. Among pigmentary disorders, vitiligo and halo area of halo nevus were characterized by an abscence or marked reduction in the number of dopa-positive cells, but lentigo and cafe-au-lait spot were characterized by an increase in their number In tuberous sclerosis, tinea versicolor and idiopathic guttate hypomelanosis, there wasn't any change of the melanocyte population between lesional skin and normal skin. The significance of these findings in vertical skin sections was discussed.