BACKGORUND: The objective of this study was to investigate the conditions required for tracheal intubation and the responses to intubation after the administration of a high concentration of sevoflurane- N2O-O2 for vital capacity rapid inhalation induction (VCRii) without muscle relaxant. We compared those with propofol-N2O-O2-vecuronium induction. METHODS:Fifty ASA physical status i or ii adult patients without airway abnormalities who were scheduled for elective surgery requiring endotracheal intubation were randomly allocated to receive either propofol 6g/ml target controlled infusion-N2O 4 L/min-O2 2L/min-vecuronium 0.12mg/kg iv (group PV) or 8% sevoflurane-N2O 4 L/min-O2 2L/min without muscle relaxant (group SO). Vecuronium was injected ninety seconds after starting propofol infusion in group PV. Group SO patients were coached on how to perform vital capacity breathing and the breathing circuit was primed for 2 minutes. Five minutes after the administration of induction agents, intubation was attempted. intubation conditions, arterial blood pressure (BP) and heart rate (HR) changes accompanying both induction techniques were monitored. RESULTS: The time to loss of consciousness for group SO was significantly shorter (41.0+/-15.0 sec vs 81.8+/-25.8 sec, P = 0.000). intubation was successful in 24 out of 25 patients (96%) in group PV and 25 out of 25 patients (100%) in group SO, and clinically acceptable intubating conditions were obtained in 23 of the 25 patients (92%) in group PV and 21 of the 25 patients (84%) in group SO. Significant decreases in BP from baseline were observed before intubation in both groups. The increase in BP at 1min after intubation was significantly greater in group PV. HR did not differ in the two groups. CONCLUSiONS: The intubation conditions after sevoflurane-N2O-O2 without muscle relaxant were similar to those produced after propofol-N2O-O2-vecuronium. Sevoflurane-N2O-O2 VCRii is a useful alternative technique for tracheal intubation when muscle relaxant should be avoided.