Vulnerable neurons in the hippocampus die 2-3 days after transient global brain ischemia. In the present study, rat brain mitochondria were isolated at different time points (4 h, 24 h and 48 h) after transient global ischemia. Detection of mitochondrially-generated reactive oxygen species, measured through dichlorodihydrofluorescein oxidation, was increased up to 40% relative to control in hippocampal mitochondria at 4 h and 48 h of reperfusion. Ischemia-stimulated oxidative stress was observed with mitochondria oxidizing substrates linked to nicotinamide adenine dinucleotide or flavin adenine dinucleotide, but not in the presence of the respiratory chain inhibitor antimycin A. A slightly decreased Ca2+ uptake capacity was observed in hippocampal mitochondria during reperfusion. We conclude that transient brain ischemia induces oxidative stress in hippocampal mitochondria. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.3342111114