Apoptosis may be an important mechanism of cell death in some experimental disease models as well as in human neurodegenerative disorders. We report evidence to indicate apoptosis in the substantia nigra of Parkinson's disease patients. We studied the midbrains of 7 patients with late onset PD, 4 patients with young onset PD and 6 control subjects using the nick-end labeling method. Intense nuclear staining indicating apoptotic process was observed in 8 out of 11 parkinsonian patients studied. Apoptosis may be a contributor to the nigral neuronal death in Parkinson's disease (PD).