Subacute sclerosing panencephalitis (SSPE) is associated with inflammatory infiltration, neuronal loss, and demyelination. The pathogenesis of these changes is unclear. We examined DNA fragmentation and Bcl-2 expression in brain biopsies of nineteen SSPE patients to investigate the role of apoptosis in tissue damage. DNA fragmentation was present in oligoden-droglia, and, in tissues with neuronal loss, in neurons. Reactive astrocytes had no DNA fragmentation, but strong Bcl-2 expression. These results suggest apoptosis as one of the mechanisms for oligodendroglial and neuronal death in SSPE.