['Acute liver failure (ALF) is a significant cause of liver transplantation. We have previously reported that human herpesvirus-6 (HHV-6) was found in most livers of patients with ALF of unknown origin ending up with liver transplantation. In this study, we investigated the posttransplant HHV-6 infection of the liver graft in these patients.', 'Thirty-two patients transplanted due to ALF were included in this retrospective study. Twelve of the 15 patients with unknown cause and four of 17 patients with a known cause of ALF had HHV-6 antigens in the explanted liver. Altogether, 18 patients had some pretransplant evidence of HHV-6. After transplantation, the patients were frequently monitored for the viruses, and biopsy histology was performed in every case of graft dysfunction. HHV-6 was demonstrated in liver tissue by immunohistochemistry.', 'During the follow-up of 6 months, hepatic HHV-6 infection was demonstrated in 9 of the 18 patients, at a mean 19 days (6-38 days) after transplantation. All patients with posttransplant HHV-6 showed graft dysfunction. In biopsy histology, seven out of these nine patients demonstrated viral infection, one of them also having CMV antigens in the liver. None of those patients without evidence of pretransplant HHV-6 showed HHV-6 in the posttransplant biopsies. Posttransplant HHV-6 was not treated and the virus had no effect on 1-year patient or graft survivals.'] Is pretransplant human herpesvirus 6 infection of patients with acute liver failure a risk factor for posttransplant human herpesvirus 6 infection of the liver?