Variation of incidence of HBe antigen (HBeAg) and HBe antibody (anti-HBe) was examined by use of RIA in 72 patients with HBsAg positive liver diseases. 1) Percentage of positive HBeAg was highest (71.5%) in chronic active hepatitis with lobular distortion, followed by chronic active hapatitis without lobular distortion (70.0%) and acute hepatitis in asymptomatic HBsAg carriers (66.7%). In contrast, it was low in chronic inactive hepatitis (35.7%) and liver cirrhosis (38.5%). None of liver cancers showed HBeAg positive reaction. 2) Percentage of positive HBe antibody (anti-HBe) was highest in liver cancer (100%), followed by liver cirrhosis (61.5%) and chronic inactive hepatitis (50.0%). In acute hepatitis from asymptomatic HBsAg carriers no anti-HBe was found. In chronic active hepatitis the percentage of positive anti-HBe was low, 21.4 and 30.0% with and without lobular distortion, respectively. 3) In 45 patients with persistently positive HBsAg liver diseases, fluctuations of HBeAg and anti-HBe were followed over a period of one year in relation to serum GPT values, an indicator of clinical conditions. Serum GPT tended to fluctuate or to remain high in patients with persistently positive HBeAg or with sporadically positive HBeAg or anti-HBe, whereas it tended to become low or normal with persistently positive anti-HBe or with seroconversion from HBeAg to anti-HBe. However, there were some exceptions to this tendency. From these results we concluded that it is clinically of significant value to determine HBeAg and anti-HBe levels for the effective assessment of the activity and time course of HBsAg positive liver diseases.