To investigate the susceptibility of chronic symptomless HBsAg carriers to the hepatotoxic effect of ethanol 296 such carriers were followed up for 3 1/2 years with repeated biochemical and clinical examinations. A control group of HBsAg-negative blood donors matched by age, sex, occupation, duration and type of ethanol intake, and state of nutrition were followed up for the same period. Chronic symptomless HBsAg carriers seemed to be at risk of hepatic abnormalities when drinking an amount of ethanol which was harmless for HBsAg-negative subjects (less than 80 g). It may therefore be advisable to suggest complete abstinence from ethanol for HBsAg carriers.