The effectiveness of addition of interferon-alpha (IFN-alpha) to zidovudine in patients with AIDS-associated Kaposi's sarcoma was assessed in a non-randomized, phase II clinical trial. Twenty-one patients were treated with oral zidovudine (600 mg daily) and IFN-alpha was increased to 18 MU daily for another 4 weeks. Only one of the 20 evaluable patients achieved a partial response at 8 weeks, that lasted for 3 months. Despite IFN-alpha dose escalation in six patients, no further responses were seen. While myelotoxicity was mild, fatigue was the dose-limiting side-effect that prevented dose escalation in seven eligible patients. The combined treatment did not result in a decrease in HIV-Ag. In summary, our results indicate that the addition of IFN-alpha to zidovudine in patients with AIDS-associated Kaposi's sarcoma is not an efficacious treatment.