1. The concentration in plasma of fibrinogen derivatives fibrinopeptide A (FPA) and B beta 1-42 and the platelet release products beta-thromboglobulin (beta TG) and platelet factor 4 (PF4) have been determined in patients with acute and chronic liver disease. 2. In 21 patients with fulmiant hepatic failure on admission in grade III or IV coma the plasma FPA, B beta 1-42, beta TG and PF4 levels were significantly increased compared with those in normal control subjects. On heparinization before haemoperfusion the FPA levels returned to the normal range and during resin and charcoal haemoperfusion there were no significant changes in the coagulation or platelet factors, except for a small increase in FPA with charcoal haemoperfusion. 3. In ten patients with compensated chronic liver disease there was a significant increase in B beta 1-42 and beta TG levels but not FPA and PF4 as compared with normal controls. 4. Interpretation of the results is complicated by the possible reduced clearance of these proteins as a result of renal failure in some of the patients with fulminant hepatic failure and also by the damaged liver itself. However, these results have confirmed that disseminated intravascular coagulation can occur in both acute and chronic liver disease.