Donor cellular debris contains fragments of nuclei with genetic material.The question arises whether the amount of donor graft released DNA accumulating in the recipient lymphoidtissues after transplantation could be a measure of donor organ damage caused by ischemia and preservationas well as rejection. We found that donor heart passenger cells do not contribute to the DNA disseminatedin the recipient. All donor DNA was, then, derived from the damaged graft cells. Immediately and 1 dayafter transplantation, it was present in blood (plasma and cells) to accumulate later in the spleen.Higher values of donor DNA in the syngeneic than allogeneic combination, most evident on day 7, werepresumably due to better perfusion of graft not undergoing rejection. Immunosuppression attenuated donorDNA release and accumulation in recipient tissues, nevertheless, relatively high concentrations couldstill be detected. Further studies are in progress on the usefulness of measuring DNA concentration forevaluation of the graft damage.