The aim of this study was to evaluate the involvement of mitochondrial membrane permeability transition (MPT) after hypoxia-ischemia (HI) in 7-day-old rats. [¹⁴C]2-deoxyglucose (DOG) was administered to controls, and at various time points after HI. MPT in the cerebral cortex was measured as entrapment of DOG-6-P in mitochondria. Another group of rats was treated with the MPT inhibitor cyclosporin A (CsA; 10–50 mg/kg i.p.) or vehicle before and after HI, and the effect on brain injury and mitochondrial respiration was evaluated. A significant increase in DOG-6-P entrapment in mitochondria indicated that MPT occurred in two phases: a primary MPT after 0–1.5 h and a secondary MPT after 6.5–8 h of reperfusion. However, CsA did not affect brain injury or mitochondrial respiration. The data suggest that MPT occurred after HI but does not provide evidence for its involvement in the development of injury.