Interferons are natural proteins with important regulatory functions. Impairment of their production may help to explain many of the immunologic abnormalities and disease susceptibilities of AIDS patients, while excessive production of an unusual type of interferon may explain some of the systemic symptoms associated with the syndrome. In a subset of patients, alpha interferons may have therapeutic potential against a major complication of the syndrome, Kaposi's sarcoma. Finally, both alpha and gamma interferons have potential, but as yet unexplored roles to play in the treatment of HTLV-III/LAV viremia and in the control of secondary infectious complications of the syndrome.