Plasma glutathione levels were determined in 79 patients with various types of liver disease and 18 healthy controls in order to study their significance in the course of liver disease. Plasma was taken at the time of needle liver biopsy. A positive linear correlation was found between plasma and hepatic glutathione concentrations, as has been suggested in experimental animals. In patients with acute viral hepatitis, chronic hepatitis, non-alcoholic liver cirrhosis and alcoholic liver disease, plasma glutathione levels were significantly decreased compared with those in controls. Of importance is the fact that the plasma levels increased after recovery in patients with acute viral hepatitis and after abstinence from alcohol intake in patients with alcoholic liver disease. Determination of plasma glutathione may be valuable in the evaluation of liver disease, particularly in acute viral hepatitis and alcoholic liver disease in which the hepatic content of glutathione is suggested to be decreased. Such patients may be susceptible to oxidative stress and radical-related hepatic injury.