To date, the significance of chimerism has not been fully understood. In particular, microchimerism can be associated with allograft acceptance or rejection. Several factors may influence the immunologic consequences of chimerism. In this review, the major factors influencing these consequences are briefly described. Subsequently, the different methods available for detecting and tracking donor-derived cells are listed. These techniques have been mainly developed concomitantly with nonmyeloablative hematopoietic allografts to monitor immunosuppression. Finally, the authors suggest how these methods may help to improve the understanding of microchimerism in solid organ transplantation.