QT dispersion is defined as the difference between QT (max) and QT (min) in the 12-lead surface EGG. It has been shown to reflect regional variations in ventricular repolarisation and is significantly greater in patients with arrhythmic events than in those without them. The aim of this study was to examine the effects of halothane and sevoflurane on QT and QTc dispersion during inhalational induction of anaesthesia. The effects on QT and QTc dispersion of halothane and sevoflurane have been investigated during induction of anaesthesia. Forty-six ASA (American Society of Anaesthesiologists) physical status I-II patients, aged 16-50 years, undergoing general anaesthesia were randomly allocated to receive either halothane or sevoflurane. The mean baseline values for QT and QTc dispersion were not significantly different between the two groups (P > 0.05). QT dispersion was increased with halothane compared with baseline values (50 +/- 16 ms vs. 29 +/- 9 ms, P < 0.01) and after sevoflurane compared with baseline (48 +/- 15 vs. 33 +/- 8 ms, P < 0.01). Also, QTc dispersion was increased with halothane compared with baseline values (48 +/- 13 ms vs. 31 +/- 9 ms, P < 0.001) and after sevoflurane compared with baseline (50 +/- 14 vs. 40 +/- 11 ms, P < 0.01). The QTc interval did not change by both sevoflurane (443 +/- 7 vs. 431 +/- 21 ms, P > 0.05) and halothane (419 +/- 33 vs. 431 +/- 19 ms, P > 0.05) compared with baseline. Both halothane and sevoflurane cause myocardial repolarisation abnormalities in man in terms of increased QTc dispersion. This may be relevant in the aetiology of arrhythmias in patients during anaesthesia with halothane or sevoflurane.