We propose to characterize the dementia which complicates the acquired immune deficiency syndrome (AIDS) with respect to clinical profile, diagnostic approach, natural history, etiology and pathogenesis. Dementia is now being recognized as one of the most common and most devastating complications of AIDS. At present neither the etiology nor pathogenesis of AIDS dementia is established. Clinical characterization of dementia and other central nervous system (CNS) disorders complicating AIDS will be accomplished by a prospective study of newly diagnosed AIDS patients as well as by a thorough analysis of patients with overt neurological impairment. Patients will undergo standardized evaluation including neurological examination, extensive neuropsychological testing, and neurodiagnostic studies including CT or MRI scan and CSF analysis. The hypothesis that AIDS dementia is due to direct CNS infection with HTLV-III will be pursued using viral culture, immunohistochemical staining of viral antigens, and viral nucleic acid hybridization to evaluate brain tissue obtained at autopsy. Positron emission tomographic (PET) scanning and analysis of neurotransmitters will be used to investigate the pathophysiology of brain dysfunction in these patients. These studies will provide a rational basis for the development and evaluation of efforts to prevent and treat this devastating complication of AIDS.