Skin samples taken from 6 female patients receiving allogeneic bone marrow transplants (BMT) from male siblings (n=5) or from unrelated human leukocyte antigen (HLA)-matched male donor (n=1) due to hematological malignancies were studied for the presence of donor cells. One nontransplanted male and 1 female control that received female BM were used as further controls of the technique. Skin biopsies were taken from the scalp and the back from each patient 12-16 years after the successful BMT. We have found donor chimerism in all of the 6 patients in both of their biopsies. Using single and double immunostainings in combination with Y chromosome hybridization, we observed that there are cytokeratin-expressing donor-derived cells in the epidermis of all the 6 patients, the numbers being slightly higher in the scalp (0.37%-1.78%) than in the back (0.32%-1.08%) biopsies. The indication for BMT, and the age of the patient did not seem to have any effect on the numbers found. A few of the double-labeled cells also stained for Ki67, a marker of cellular proliferation, suggesting that the engrafted cells were able to further divide in the epidermis. In 2 patients we observed patches of donor keratinocytes within the epidermis, suggesting a clonal origin. We conclude that in agreement with some and in contrast to other published studies, BM-derived circulating cells are able to engraft in the human skin and to further proliferate there and thus contribute to tissue renewal. These data raise the possibility to use BM cells in regenerative medicine to help in extended injuries, large surface burns, or lack of skin due to other reasons.