The involvement of cytosolic phospholipase A2 (cPLA2) in apoptosis of adult mouse superior cervical and dorsal root ganglia neurons has been investigated by the use of immunohistochemistry for cPLA2 and DNA nick-end labeling for apoptotic cells, respectively. cPLA2 immunoreactivity was strongly upregulated in neurons of both preparations during in vitro culturing. By double labeling it was unequivocally demonstrated that cPLA2 was present and upregulated only in neurons undergoing apoptosis. A similar picture emerged when cPLA2 immunoreactivity was compared with staining with Fluoro-Jade, a novel fluorochrome marker for neuronal degeneration. The preferential presence of cPLA2 in apoptotic and degenerating cells suggests that the enzyme is important for some mechanism involved in or intimately coupled to neuronal cell death.