Paraffin sections from the hippocampus, the cingulate gyrus and the insula of 18 head-injured patients who survived between 5 hours and 10 days, and 18 age-matched controls, were stained by the terminal deoxynucleotidyl transferase mediated biotinylated deoxyuridine triphosphate nick end labelling (TUNEL) technique for evidence of in situ DNA fragmentation. Additional staining techniques (HE, combined LFB/CV and immunohistochemistry for GFAP and CD68) were used to characterize any lesions and their time course. Only the occasional TUNEL+ cell per area was seen in the control brains. TUNEL+ cells were identified in both grey and white matter of the head-injured material and their numbers peaked between 24 and 48 hours and were still present at 10 days. Within the hippocampus, fewer TUNEL+ cells were seen in grey (between 3-5 per area) than in the white matter, (up to 51+ per area) whereas in the cingulate gyrus and in the insula, the number of TUNEL+ cells was always greater in the cortex (between 11-20 per area) than in white matter (6-10 per area). In the grey matter, most TUNEL+ cells had the morphology of necrosis. However, the histological appearances of some of the neurons (2-3%), and of oligodendroglia and macrophages in white matter (about 5%) were those of apoptosis.