The epidemiology, clinical and pathologic manifestations, identification of groups at high risk, results of laboratory analyses, and description of the modes of transmission of the putative etiologic agent HTLV-III/LAV have been summarized. Mechanisms of induction of T-cellular immunodeficiency have been described, including the role of HTLV-III/LAV, and possible roles of CMV and EBV as cofactors have been presented. Prospects for preventing and treating AIDS have been succinctly summarized.