The efficacy of recombinant leukocyte A interferon (rIFN-alpha A [Roferon-A, Hoffman-La Roche, Nutley, NJ]) treatment of Kaposi's sarcoma in patients with acquired immunodeficiency syndrome was evaluated in sequential trials using high doses (36 X 10(6) units) and low doses (3 X 10(6) units) of interferon. A major response was seen in 38% of patients treated at the high dose, with a median response duration of 18 months. At the low dose, the major response rate was 3%; dose escalation to 36 X 10(6) units resulted in an additional major response rate of 17% in low-dose nonresponders, with a median response duration of 10 months. Four of 11 patients who achieved a complete response remain free of disease, whereas all partial responders have shown disease progression. Unacceptable toxicity occurred in 27% of patients initially treated at the high dose and only in 10% of those who had progressive dose escalation up to 36 X 10(6) units. Prior opportunistic infections correlated negatively with therapeutic response, whereas large tumor burden and gastrointestinal involvement did not. Responding patients showed a significantly longer survival and a lower incidence of subsequent opportunistic infections than nonresponders. However, from our study we cannot determine whether rIFN-alpha A has an effect on the natural history of Kaposi's sarcoma in patients with the acquired immunodeficiency syndrome.