Raised plasma carcinoembryonic antigen (CEA) levels were found in over 90% of 71 patients with chronic liver disease and 50% of 16 patients with acute liver damage. Levels increasing chronicity and clinical severity of disease. In individual patients, the plasma CEA level fluctuated with the clinical condition. Persistently normal levels were never found in patients with chronic liver disease in poor clinical condition. A very high level suggests a bad prognosis. If CEA is considered together with SGPT, a discriminant function can be calculated, separating patients with acute liver damage and those with an acute exacerbation of chronic active hepatitis, with a high degree of certainty. In acute damage, peak CEA levels occur later than the time of maximum liver necrosis, suggesting that the rise is not owing to release of CEA from damaged cells. There is no significant difference in CEA level between patients with and without spontaneous or surgical portosystemic shunts, suggesting that high levels are not attributable to bypass of the liver. The timing of the rise in CEA in acute liver damage suggests that raised levels may be associated with regeneration. The tendency for higher levels to occur in those patients with greater disturbances of liver function suggests altered metabolism or excretion of CEA.