Cell-to-cell interactions between human mesenchymal stem cells and potential adjacent cells such as endothelial cells, dermal fibroblasts, and epidermal keratinocytes was investigated. A modified dual Boyden chamber assay using 8-microm pores revealed a more powerful chemotactic cell migration of human mesenchymal stem cells toward human epidermal keratinocytes than other cells, such as umbilical artery endothelial cells and dermal fibroblasts, during 16 hours of incubation (336.2+/-52.33, 36.0+/-11.20, and 62.7+/-18.16, cells/field, respectively, p<0.01; comparison between endothelial cells and keratinocytes, and fibroblasts and keratinocytes). Scanning electron microscopy showed human mesenchymal stem cell migration through the pores, with endothelial cells, fibroblasts, or keratinocytes in the lower chambers. Mesenchymal stem cell ultrastructural changes occurred, including a larger euchromatin nucleus, when the cells were placed in medium containing 10 percent fetal bovine serum, whereas basic fibroblast growth factor maintained the immature cell morphology for 4 days. Monolayer coculture also showed human mesenchymal stem cell changes in ultrastructural morphology in the vicinity of the epidermal keratinocytes. These data suggest that human mesenchymal stem cells may interact with human epidermal keratinocytes to accelerate wound healing and coverage.