47 HIV-positive male patients with cutaneous Kaposi's sarcoma (KS) were treated with recombinant interferon alpha-2A (IFN) in an open, prospective study. 45 patients received 18 million I.U. IFN s.c. daily for the first three months. From the fourth month, the patients received 18 million I.U. IFN s.c. three times weekly. Four of the 45 patients withdrew from therapy because of side effects during the first weeks (weeks 2 to 6) of treatment. The remaining 41 patients were treated for a minimum period of two years or until their death. Two further patients received 36 million I.U. IFN daily for three months. After three months of IFN therapy we observed complete remission (CR) in five of the 41 patients (12%), partial remission (PR) in seven patients (17%), stable disease in seven patients (17%) and progressive disease (PD) in 22 patients (54%). The mean survival time from the beginning of IFN therapy to date is 26 months for the 19 responders (patients with CR, PR or SD; six are still alive) and nine months for the 22 non-responders (patients with PD; all died). Recurrence of tumor progression occurred in 15 of the 19 responders after an average of ten months of continuous IFN therapy. The longest time of survival in this group is 54 months up to now. Of the four remaining patients, all in the CR group, two died after 24 and 26 months of IFN therapy, without any recurrence of KS growth (causes of death: Burkitt's lymphoma and unknown). The two other patients, both still alive, have not suffered any recurrence of tumor progression after 40 and 41 months, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)