To test the hypothesis that apoptosis is involved in human brain neurodegenerative disorders, we investigated whether DNA fragmentation occurs in Alzheimer's disease (AD). Huntington's disease (HD) and Parkinson's disease, as well as in temporal lobe epilepsy, using neurologically normal post-mortem human brain tissue as a control. Using in situ end labelling of DNA, we found evidence of DNA fragmentation in cells in temporal cortex and hippocampus from patients with AD and in striatum from those with HD. In contrast, only scattered DNA fragmentation positive cells were detected in the pial surfaces of some of the neurologically normal human brains. Thus, cells in the HD striatum and AD temporal cortex exhibited DNA fragmentation, suggesting that apoptosis may be involved in these disorders.