BACKGROUND: Induction of anesthesia with propofol caused a decrease in arterial blood pressure and systemic vascular resistance. This effects of propofol on the circulation can be more clarified by studying cardiovascular control mechanism such as baroreflex sensitivity during variable rate infusion of propofol. METHODS: The effects of three infusion rates of propofol (3, 6, 12 mg/kg/hr) to supplement 66% nitrous oxide in oxygen anesthesia on baroreflex sensitivity were studied and compared with awake value in 80 ASA I or II patients (20-55 years old, n=20 in each group). Baroreflex control of heat rate was studied by pertubing the patients' arterial pressure with 100 microgram of phenylephrine in each three infusion rates of propofol which was maintained at least 30 min without any surgical stimulation. RESULTS: Baroreflex slope representing baroreflex sensitivity among three infusion rates of propofol did not show any significant differences. The slope of each infusion rate was 8.4+/-0.7 at awake, 8.9+/- 1.7 at 3 mg/kg/hr, 8.0+/-1.3 at 6 mg/kg/hr, 7.2+/-1.0 at 12 mg/kg/hr, respectively. But, resetting of the reflex occured at low heart rates. CONCLUSIONS: Usual propofol-nitrous oxide-oxygen anesthesia was not associated with impairment of baroreflex sensitivity, but showed reflex resetting at low heart rates.