Previous reports have shown the effectiveness of a basal layer cell suspension in the treatment of stable vitiligo; however, there has been no mention in the literature until now of the optimal number of melanocytes required in an autologous noncultured epidermal suspension for transplantation to obtain early and acceptable results. In this randomized prospective study, we compared the efficacy of two different dilutions to determine the optimum density of melanocytes required for transplantation to achieve early and cosmetically acceptable results. We enrolled 20 patients with stable vitiligo with a body surface area involvement of< 10%. Fifty per cent of patients in Group A (where the recipient area transplanted was approximately three times the size of the donor area, and the density of melanocytes transplanted per square millimeter was approximately 231.60+/- 27.03) showed marked (> 75%), 20% moderate, 10% mild, and 20% minimal repigmentation (or no response). In Group B (where the recipient area was increased to five-fold the donor area), none of the patients showed marked, 10% showed moderate, 20% showed mild, and 70% showed either minimal or no repigmentation. The density of melanocytes transplanted in this group was 154.90+/- 27.65/mm(2). The extent of repigmentation was significantly greater (P< 0.05) in Group A than in Group B, and the density of melanocytes in the suspension was also significantly greater (P< 0.01) in Group A than in Group B. We contend that the minimum number of melanocytes required to produce satisfactory repigmentation is probably in the range of 210-250/mm(2).