In liver, apoptosis is a physiological process involved in the clearance of injured cells and in homeostatic control . However, in patients with viral fulminant hepatitis or with nonacute liver diseases , dramatic liver failure or secondary cirrhosis results from the death of hepatocytes, which express the cell-surface receptor Fas, by apoptosis. To date, treatment of fulminant hepatitis relies mainly on orthotopic liver transplantation, which is limited by immunological complications and graft availability. Unravelling the molecular mechanisms that underlie acute liver failure could allow the design of an appropriate therapy. Ligand-bound Fas and tumour necrosis factor alpha (TNF-alpha) induce hepatic apoptosis in mice [3-6]. In various cell types, Fas- or TNF-alpha-induced apoptosis is blocked by viral proteins (such as p35 and CrmA) as well as by a decoy peptide (YVADcmk) [7-11], suggesting that these mechanisms of apoptosis involve ICE (interleukin-1 beta converting enzyme)-like proteases. Here, we report that, in vivo, pre-treatment of mice with YVADcmk protects them from the lethal effect of anti-Fas antibody and from liver failure induced by injection of TNF-alpha. Remarkably, YVADcmk administration is also highly effective in rescuing mice that have been pretreated with anti-Fas antibody from rapid death, despite extensive hepatic apoptosis. This dramatic curative effect could be of clinical benefit for the treatment of viral and inflammatory liver diseases.