Three hundred and eighty-five patients mostly with chronic liver diseases and 729 apparently healthy adults were studied for hepatitis B surface antigen (HBsAg) with reversed passive hemagglutination and antibody (anti-HBs) with passive hemagglutination. In healthy adults around 15% was HBsAg positive and in 45% was anti-HBs positive, estimating hepatitis B virus (HBV) infection in nearly two thirds of the population. The infection already occurred before adulthood. The prevalences of HBsAg were invariably over 80% in chronic hepatitis, cirrhosis and hepatocellular carcinoma (hepatoma) indicating an intimate relationship to HBV. On the contrary, the positive rates of anti-HBs in these diseases were far lower than those in healthy people and patients with other diseases, this is similar to the situation in chronic HBsAg carriers. The prevalence of HBsAg in hepatoma patients was unusually high, being 82.7% in contrast to 11.9% in patients with other malignancies. Not only hepatoma patients with cirrhosis but also those without cirrhosis were found to have high prevalence of HBsAg. The fact indicates an even more intimate relationship between hepatoma and HBV.