It has been shown that satellite cells can be successfully isolated and expanded in vitro from fetal and adult muscle biopsy . In order to create a tissue in vitro that can be reimplanted in vivo, donor cells must be autologous or at least nonimmonogenic . Therefore, primary satellite cells or other stem cells, which can differentiate into skeletal muscle cells, are the ideal source for transplantation approaches in muscle tissue engineering. One major problem that cell transplantation studies imitating autologous transplantation are facing at the moment is the ability of detecting transplanted cells after integration in the host. Therefore we developed an approach to create functional skeletal muscle tissue in vivo using the transplantation of primary myoblasts precultivated within a three-dimensional (3D) fibrin matrix and to determine the fate of the transplanted cells using the Y chromosome detection technique in a syngeneic rat animal model . 3D myoblast cultures were established derived from male donor rats and after 7 days of cultivation we performed an orthotopic transplantation of 3D-cell constructs into a created muscle defect within the gracilis muscle of syngeneic female rats (Fig 2A). These transplanted cells showed a poitive desmin immunostaining, supporting the assumption of the cells retaining their myogenic phenotype and Y chromosome in situ hybridization indicated the survival and integration of transplanted male myoblasts into the female recipient animal (Fig. 2B). After 50 days male donor cells still could be tracked, now as Y chromosome positive nuclei incorporated into host tissue, resulting in several mosaic multinuclear muscle fibers, consisting of cells of male and female origin (Fig 2C,D). These fibers were restricted to the area around the implantation site of the 3D-cell construct, indicating that transplanting myoblasts in a syngeneic rat model results in regeneration of skeletal muscle fibers by incorporation of myoblasts into host myofibers (Fig. 2C,D). Thus this approach to tissue engineering, transplantation of a small number of cells and growing the tissue in vivo, may bypass current difficulties in the in vitro engineering of large tissue masses for subsequent transplantation that are related to the lack of sufficient vascularization. Moreover this approach may be ideal for the utilization of small numbers of stem cells in the regeneration of skeletal muscle tissue . In summary, further progress in stem-cell technology , as well as discovery of conditions responsible for the control-mechanisms of proliferation and differentiation of adult satellite cells, combined with suitable techniques of vascularization might allow for the production of autologous artificial skeletal muscle-like tissue that is capable of correcting muscle injury and restoring impaired muscle function.