Strong c-Jun immunoreactivity, but not c-Fos expression, was observed in typical apoptotic cells in medulloblastomas, central neuroblastomas, malignant astrocytomas and glioblastomas, and in lymphocyte-like cells bearing nuclear fragmented DNA in medulloblastomas. In contrast, only a few proliferating cells, as revealed with PCNA immunohistochemistry, colocalized c-Jun. These results support the concept that strong c-Jun expression is associated with certain forms of cell death in human tumors of the central nervous system.