Anti-idiotype monoclonal antibodies are now available for up to one-third of all patients with B-cell cancer. This is because some antibodies made in the past for individual patients cross-react with the idiotype expressed by other patients' tumor cells. Clinical trials with anti-idiotype antibodies have demonstrated reproducible antitumor effects in patients who have failed conventional treatments. The anti-idiotype antibody treatments are not associated with any significant toxicity and rarely induce immune responses in patients with B-cell lymphoma. They can therefore be used repetitively. Future developments will include the combination of anti-idiotype antibodies with other biologic therapies and with chemotherapy. In addition, one may be able to induce the patient to make an active immune response against the idiotype expressed by his or her tumor cells.