Tissue chimerism was recently described in transplanted organs from female donors into male recipients, by demonstration of the Y-chromosome in tissue-derived cells. It was claimed that these Y-chromosome positive cells were recipient derived. To find out whether the chimeric cells, derived from pregnancies of sons or blood transfusions, could have been present in the solid organs before transplantation, we performed the following study. In situ hybridization for the Y-chromosome was performed on the normal organs (51 kidneys, 51 livers, 69 hearts) from 75 women of the normal population, whose child and blood transfusion status were known. Chimeric cells were found in 13 kidneys, 10 livers and 4 hearts, of 23 women. There was no relation between the child status or the blood transfusion history with the presence of Y-chromosome positive cells. We have for the first time demonstrated that male cells are present in normal kidneys, livers and hearts. Theoretically, these organs could have been used for the transplantation. Therefore, our findings demonstrate that the chimeric cells thus far described in transplantation studies, are not necessarily donor derived, and could have been present in the organs before the transplantation.