Four patients who received an auxiliary partial liver graft for decompensated liver cirrhosis due to hepatitis B (HBV), associated in two cases with hepatitis D virus (HDV) superinfection, were studied. The sequential appearance of hepatitis B and D antigens in the grafts was investigated in serial liver biopsies by immuno-histochemical methods and compared with the viral antigenic profiles of the host livers. The histological changes in the liver grafts were studied in relation to the viral expression patterns. One week after transplantation, expression of HBsAg was already apparent in two grafts. HBcAg was found in the graft of the only patient with HBcAg in the host liver. HDAg was expressed in the grafts of both patients with HDV superinfection; in one of these cases HDAg was present without HBsAg. At 3 months, viral antigen expression was maximal. Expression of HBsAg and HBcAg in the grafts of the two HDV-positive patients was, however, less extensive than in the two HBV-positive patients. All patients developed a mild lobular hepatitis, histologically demonstrated between the 47th and 107th posttransplantation day. In the two HBV-positive, HDV-negative patients, cirrhotic transformation of the graft occurred within 1 year. In the HDV-positive patients only a mild chronic active hepatitis with slight or moderate fibrosis was observed after 1 year. We conclude that recurrence of HBV and HDV infection in auxiliary liver grafts is demonstrable within 1-3 weeks. HBV infection in liver grafts may be a rapidly progressive disease. Coinfection with HDV does not aggravate the acute hepatitis and may even suppress the progression of chronic HBV.