Asymptomatic carriers of hepatitis B surface antigen (HBsAg) were surveyed for serum e antigen (e Ag) and antibody to e (anti-e) by immunodiffusion. Seventeen serum samples containing e Ag and 17 containing anti-e, but with similar HBsAg titers, were tested for the presence of hepatitis B core antigen (HBcAg) by means of immune adherence hemagglutination method. HBcAg activity was detected in all of the samples containing e Ag, and the titer of HBcAg paralleled that of HBsAg in each serum. In remarkable contrast, no HBcAg activity was found in any of the serum samples containing anti-e. Dane particles were demonstrated in 14 of 17 serum samples with e Ag by electron microscopy, but in none of 17 with anti-e. Although both e Ag and HBcAg were closely associated with each other, the non-identity of e Ag and HBcAg was clearly demonstrated by a two-dimensional immunodiffusion test.