The value of coagulation factor V and VIII/V levels as prognostic indicators was assessed in 27 patients with fulminant hepatic failure and compared with other predictive indices. Admission factor V levels were significantly reduced in 22 patients with paracetamol induced hepatic failure compared with a healthy control group (median 9.5% v 103%, respectively; p less than 0.001) and with lower values in non-A non-B hepatitis (median 2.7%). Values in the seven patients who died after paracetamol overdose, considered together with the four who underwent liver transplantation (group median 5.1%), were significantly lower than in the 11 who survived (median 11.8%; p less than 0.01). Median admission factor VIII was higher in those who died or received a transplant than in those who survived (298% v 162%; p less than 0.05), with both results higher than in healthy volunteers (median 104%; p less than 0.01) but lower than in non-A non-B hepatitis (median 340%). The ratio of factor VIII/V on admission was less than 30 in all patients who survived paracetamol overdose (median 17) with corresponding values greater than 30 in 10 of 11 of those who died (median 39). A factor V result less than or equal to 10% on admission predicted an adverse outcome in 10 of 11 fatal cases, a 91% sensitivity which was greater than for the previously defined indicator of an arterial blood pH less than 7.30 on admission (sensitivity 82%). Prothrombin time at admission or on day 4 did not usefully predict outcome in our series. Predictive accuracy was 73% and 82% for factor V and admission acidosis respectively and 95% for factor V in conjunction with admission coma grade III or IV and factor VIII (ratio > 30). These criteria may be useful in selecting patients with paracetamol induced fulminant hepatic failure for transplantation.