Anti-idiotypic antibodies (anti-Id) that contain an internal image component that mimics the surface antigen of hepatitis B virus (HBsAg) were used to immunize chimpanzees. Four injections of the rabbit anti-Id preparation elicited an antibody response to HBsAg (anti-HBs). The antibody specificity appeared to be against the anti-Id, since the anti-Id immunogen was shown to bind the chimpanzee anti-HBs. Two chimpanzees immunized with the anti-Id, along with two control animals that were either untreated or received a nonimmune rabbit immunoglobulin G preparation, were challenged with infectious hepatitis B virus. Both control chimpanzees developed clinical and serological characteristics consistent with an active hepatitis B virus infection, whereas the two anti-Id treated chimpanzees were protected from infection. Since chimpanzees provide a relevant model of a human response to hepatitis B virus immunization and infection, these results indicate that anti-Id preparations such as that described here might be candidates for vaccines against human diseases.