Propofol suppresses both the sympathetic and parasympathetic nervous systems. There have been no clinical studies examining the infusion rate-related hemodynamic interaction between propofol and landiolol, an ultra-short-acting β 1- blocking agent. Twenty-four patients were divided into two groups. Patients in the P-1.25 group (n＝12) received intravenous (IV) propofol (1.25 mg / kg) over 1 min followed by continuous infusion of propofol at 5 mg / kg / h. Tracheal intubation was facilitated with IV rocuronium, and anesthesia was maintained with propofol at 5 mg / kg / h and 67% nitrogen in oxygen. Patients in the P-2.5 group (n＝12) received IV propofol (2.5 mg / kg) over 1 min followed by propofol at 10 mg / kg / h. All other protocols were identical to those in the P-1.25 group. Fifteen minutes after tracheal intubation, patients in both groups received IV landiolol at incremental infusion rates (40, 50, 60, 70, 80, 90, and 100 μ g / kg / min for 2 min at each dose). Changes in heart rate (HR) were greater in patients in the P-1.25 group than the P-2.5 group. The landiolol infusion at 40, 50, or 60 μg / kg / min caused HR changes of －6±4, －9±6, and －13±6 beats / min (bpm) in the P-1.25 group, while the HR in the P-2.5 group decreased by －1±3, －4±2, and －6±4 bpm (mean±SD, P＜0.05). When landiolol was infused at a rate of 90 μg / kg / min, HR decreased by more than 15 bpm in all patients in the P-1.25 group, but only 40% of patients in the P-2.5 group. We conclude that the HR response to IV landiolol is attenuated at higher propofol infusion rates.