In immunosuppressed patients human herpesvirus 6 (HHV-6) reactivations are common. The aim of the study was to determine to which extent HHV-6 can be found in the gastrointestinal tract in kidney transplant recipients and in patients on chronic dialysis. The HHV-6 and cytomegalovirus (CMV) examinations were performed on gastro duodenal and colon biopsy specimens obtained from 81 kidney transplant recipients and on 46 chronic dialysis patients. The HHV-6 and CMV were demonstrated by immunohistochemistry detecting both HHV-6A and HHV-6B, and CMV-specific antigens. The HHV-6B-positive cells, were found in gastroduodenal biopsy specimens from 34% of the transplant recipients and 28% of the patients on chronic dialysis, CMV-positive cells were found in specimens from 53% of the transplant recipients and 28% of the patients on chronic dialysis. The HHV-6B positive cells were found in the colonic mucosa specimens from 36% of the transplant recipients and 22% of the patients on chronic dialysis, CMV-positive cells were found in specimens from 36% of the transplant recipients and 17% of the patients on chronic dialysis. The HHV-6B positive cells were found equally often in the gastroduodenal as in the colorectal mucosa. The HHV-6B positive cells as well as CMV positive cells were simultaneously found in every fifth of transplant recipients.