To examine whether donor-derived cells could exist in nonhematopoietic tissues of recipients after allogeneic hematopoietic stem-cell transplantation, we examined the patterns of the short tandem repeat (STR) of DNA extracted from fingernail clippings of recipients so that the contamination of blood cells was excluded. All 21 patients reached donor-derived hematopoiesis after transplantation and 20 of them were in remission of the primary diseases at the time of sampling. Compared with the STRs of donor cells, among 9 of 21 patients, DNA extracted from fingernail samples showed coexistence of the donor pattern of the STRs, sharing from 8.9% to 72.9% of total STR areas. Time from transplantation to sampling was from 305 to 2399 days among positive cases. These results demonstrate for the first time the existence of stable contribution of donor cells in fingernails among recipients of allogeneic hematopoietic stem cells.