Human herpesvirus 8 (HHV-8) is a recently discovered virus that appears to have a pathogenic role in Kaposi's sarcoma, multicentric Castleman's disease, and primary-effusion lymphoma, a distinctive lymphoma that arises within body-cavity effusions.¹–⁷ HHV-8 was originally detected in lesions of Kaposi's sarcoma in patients infected with the human immunodeficiency virus (HIV) but was subsequently found in forms of the tumor that occur in HIV-negative patients.⁸,⁹ Similarly, HHV-8–associated multicentric Castleman's disease occurs predominantly in patients with the acquired immunodeficiency syndrome (AIDS) but also in HIV-negative patients.⁵,¹⁰,¹¹ These findings suggest a direct causal role of HHV-8 in the . . .