Sevoflurane has been reported to generate oxygen free radicals. We have investigated whether sevoflurane or isoflurane enhances oxygen free radical formation in the post-ischaemic reperfused heart. An isolated rat heart–lung preparation was used. Thirty male Wistar rats were allocated to four groups: control, no drug, 2.5% sevoflurane and 1.4% isoflurane. The heart was perfused initially at a cardiac output of 30 mL min−1 and a mean arterial pressure of 70 mmHg. Ten minutes after the start of perfusion, the heart was rendered globally ischaemic for 10 min by reducing the preload and afterload to zero. Then, the heart was reperfused for 10 min. At the end of reperfusion, the heart was freeze dried for 6 days. The perfusate blood was collected just before and just after ischaemia and at the end of reperfusion. The formation of hydroxyl radicals in perfusate blood and heart was measured with high-performance liquid chromatography using salicylic acid. Hydroxyl radicals react with salicylic acid, yielding 2,3-, 2,4-, 2,5- and 3,4-dihydroxybenzoic acid (DHBA). Before and after ischaemia, there were no significant differences in cardiac output, systolic pressure, heart rate and right arterial pressure among the groups. The concentrations of 2,3-, 2,4-, 2,5- and 3,4-DHBA in the perfusate blood after ischaemia and reperfusion were significantly higher than those before ischaemia in all groups. However, there were no differences in the DHBA levels among groups. This study indicates that sevoflurane and isoflurane do not enhance hydroxyl radical formation in the post-ischaemic reperfused heart.