Alpha interferon has been the most widely studied biologic response modifier for the treatment of Kaposi's sarcoma (KS) associated with acquired immune deficiency syndrome (AIDS). At San Francisco General Hospital's AIDS Clinic, three sequential trials of recombinant interferon alfa-2b (Intron A) were conducted between August 1982 and April 1984. In the first study, ten patients with early KS were randomized to receive either low-dose (1 MU/m2) subcutaneous (SC) or high-dose (50 MU/m2) intravenous (IV) treatment 5 days per week, every other week, for eight weeks. A perceived advantage of the latter regimen led to a subsequent trial in which 20 subjects received high-dose IV therapy. A 32% objective response rate was achieved, despite the fact that these patients had less favorable disease status and more constitutional symptoms than those in the first trial and had also experienced previous opportunistic infections (OIs). A final 8-week investigation evaluated the use of 30 MU/m2 three times per week in 30 subjects. Drug-related toxicity seemed more pronounced with this regimen, but overall objective responses were identical to those seen in the high-dose IV study. None of the trials produced evidence of immune reconstitution on laboratory evaluation. The patients were not protected from developing AIDS-related OI either during or following interferon therapy, although OI was diagnosed less frequently in responders, who also displayed a distinct survival advantage over those with progressive disease. These trends remained evident when the data from the three studies were pooled with those from three parallel trials conducted at the University of California, Los Angeles (UCLA). Studies evaluating the combined use of alpha interferon and chemotherapeutic agents known to be active against AIDS-related KS (such as VP-16 and vinblastine) have thus far failed to demonstrate a synergistic antitumor effect, while toxicity has increased. In light of in vitro evidence that alpha interferon suppresses the AIDS retrovirus and has clinical efficacy in KS comparable to that of cytotoxic agents, additional investigations, focusing on maximizing therapeutic potential, are warranted.