A 41-year-old man was accidentally exposed to carbon monoxide (CO) gas and found in a state of cardiopulmonary arrest while he took bath. After admission, he was resuscitated and underwent artificial ventilation in a comatose state and died about 19h later. Computed tomography (CT) examination disclosed bilateral low density area in the basal ganglia and the thalamus, a well-known finding in the CO intoxication. Necropsy, histological examination, DNA ladder assay gave the first line of evidence for the presence of apoptosis as well as necrosis in the human case of CO intoxication. TdT-mediated dUTP-biotin nick-end labeling (TUNEL) positive apoptotic cells were more predominant in the CA2 area than in CA1 area. There is general co-relation between the ratio of TUNEL-positive cells and the DNA laddering on the agarose gel. Basal ganglia and thalamus, which showed bilateral low density area in CT, were revealed to be severe edema. The two types of cell death occurred in the cortex, basal ganglia, hippocampus, thalamus, and cerebellum. Hypoxia caused by CO-hemoglobin formation alone cannot explain the phenomena.