OBJECTIVE To evaluate the clinical and biological impact of protease inhibitors on HIV-associated Kaposi's sarcoma. METHODS A cohort of 10 patients included prospectively from April 1996 to June 1997 were studied in one institutional centre after initiation of protease inhibitors. METHODS All patients but one (stable disease) had progressive Kaposi's sarcoma. Three out of 10 patients had stopped specific chemotherapy for Kaposi's sarcoma for more than 4 weeks, three were still under chemotherapy, and four had never received specific treatment of Kaposi's sarcoma. Plasma HIV viral load, human herpesvirus (HHV)-8 viraemia in peripheral blood mononuclear cells (PBMC), and CD4 cell count were sequentially assessed from the beginning of therapy. For six patients, a semiquantitative evaluation of HHV-8 viral load in the Kaposi's sarcoma lesions was performed during treatment using polymerase chain reaction. RESULTS After initiation of HIV triple therapy with protease inhibitors, we observed six complete responses, two partial responses, and two patients with progressive disease. All patients had undetectable plasma HIV viral load within 2 months of treatment. Undetectable HHV-8 viraemia in PBMC occurred in seven out of eight patients with partial or complete response and in none of the progressive patients. A decrease or negation of HHV-8 viral load in Kaposi's sarcoma lesions was observed in two complete responders. CONCLUSIONS Our results suggest that antiviral therapy with protease inhibitors are clinically efficient in HIV-associated Kaposi's sarcoma and that there exists a correlation between clinical response and negation of HHV-8 viraemia.