Several diseases are included in the category of hypomelanosis. Their clinical course as well as the pathogenesis are diverse and in many cases poorly understood. The aim of the present study is to use the nude mice model to determine whether the primary defect in various pigmentary skin disorders is inherent to the tissue itself or is secondary to systemic factors. Split-thickness skin grafts obtained from patients with vitiligo, acquired hypomelanosis guttata, and tyrosinase-negative albinism were grafted onto nude mice. Histologic examination and dopa staining were performed prior to and following the engraftment. The dopa staining was performed on the epidermal sheet following separation from the dermis. The depigmented area of the vitiligo became completely pigmented 6 to 10 weeks after skin transplantation. The dopa reaction that was negative prior to skin engraftment became completely positive after the transplantation. The number of melanocytes (expressed per square millimeter of skin surface) 8 weeks after transplantation was 197 +/- 73 mm2. Dopa reaction in acquired hypomelanosis guttata showed reduction of the number of melanocytes in the depigmented macula as compared with the surrounding area (55.25 +/- 18.00 mm2 vs 220 +/- 28.28 mm2. Twenty days after skin transplantation, repigmentation of the area was observed. The number of melanocytes increased significantly (388.75 +/- 213 mm2). The grafted skin obtained from patients with tyrosinase-negative albinism showed persistence of the depigmentation after skin transplantation. Dopa reaction was negative prior to and 8 weeks after transplantation. The results of the present study suggest that systemic factors may play a role in the pathogenesis of vitiligo and acquired hypomelanosis guttata.