Rabbit and mouse sera containing anti-idiotype antibodies against a monoclonal and against some polyclonal anti-HBsAg antibodies were prepared. The immunoglobulin fractions of these sera induced the formation of anti-HBsAg antibodies when injected into BALB/c mice. The sera of humans repeatedly immunized with human anti-HBsAg antibodies were shown to contain anti-idiotype antibodies capable of eliciting an anti-HBsAg response in BALB/c mice and Syrian hamsters. Such sera may be a potential source of human anti-idiotype vaccine.