The relevance of the recently described membrane-bound form of the HBe protein for the antiviral immune response was examined. The data show that antibodies in anti-HBe, but not in anti-HBc—positive human sera efficiently bind to the membrane expressed HBe. No evidence was obtained that the HBc can reach the cell surface in a form that can be detected with human antibodies. The findings suggest that the decline of virus titer that is usually observed after seroconversion from HBe to anti-HBe might be the result of an antibody-mediated elimination of infected cells. (HEPATOLOGY 1991;13:57–61).