It was considered that nonresponsiveness to hepatitis B surface antigen was in part due to a failure in the antigen recognition (i.e., antigens' phagocytosis, processing and presentation by accessory cells). In order to enhance the capture of antigens, we investigated the effect of simultaneous administration of HBs antigen and anti-HBs IgG on antibody responses in vitro and in vivo. As a result, in vitro sensitization of mononuclear cells from anti-HBs-positive subjects with HBs antigen and anti-HBs IgG induced significant amounts of anti-HBs IgG production in 5 of 6 cases, whereas sensitization with HBs antigen alone failed to induce the antibody production in most cases. In vivo administration of HBs vaccine and anti-HBs immunoglobulin to non-responders to the vaccine triggered active anti-HBs antibody responses in 3 of 7 cases in vivo and in 5 of 7 cases in vitro.