A patient negative for human immunodeficiency virus (HIV) developed multicentric Castleman's disease (MCD) and Kaposi's sarcoma (KS) associated with active human herpesvirus 8 (HHV-8) infection. He was treated with sequential antiviral therapy, chemotherapy, and corticosteroids. HHV-8 levels were monitored throughout the course of the patient's illness, and were found to rise on relapse. No consistent change in HHV-8 levels was found with antiviral therapy. We demonstrate that in this patient antiviral therapy was clinically ineffective, and did not alter HHV-8 levels, but that corticosteroid and combination chemotherapy led to clinical improvement. Despite the implication of HHV-8 as a cause of MCD, few studies have correlated HHV-8 levels with clinical response.