A coagulation screen has been performed on 12 patients with acute liver failure. Six died and six recovered. All six fatal cases developed a haemorrhagic state with haemostatic failure. An attempt has been made to delineate the various mechanisms for the production of the coagulation defect. The significance of the different haematological parameters in assessing prognosis has been assessed. The study emphasizes the importance of the synthetic ability of the liver in determining survival prospects. A good correlation between the factor-VII level, which is a guide to liver synthesis, and recovery has been shown. The value of a specific factor-VII assay in acute liver failure appears considerable. Where this assay cannot be performed the clot opacity fibrinogen technique provides a reasonable guide to the prognosis. The presence or absence of DIC was not a determinant factor in survival in this series.