Auxiliary liver transplantation (ALT), retaining in place the liver of the recipient, has been proposed as an alternative to liver replacement in patients with fulminant hepatic failure (FHF). Hepatobiliary scintigraphy (HS) has proved a unique tool for the separate assessment of graft and native liver function. Forty-eight HS scans were performed, following the injection of technetium-99m trimethyl-bromo-imino-diacetic acid, in six patients who underwent ALT for FHF. Quantitative parameters were derived from the time-activity curves of both the graft and the native liver. The function of the graft remained normal as long as the patients remained under immunosuppressive therapy (IST). The function of the native liver was almost completely absent in the 1st month in five patients, but it improved gradually in four of them. IST was then decreased in four patients and finally withdrawn in three. Spontaneous graft atrophy occurred in two patients and the graft was removed in two. All of the patients in whom IST was reduced had a normal global hepatic function and selective uptake (RU) >30% at that time. In ALT patients with FHF, HS can distinguish non-invasively the functional performance of both the donor and the recipient liver and its evolution with time.