In a previous study concerning balanced anesthesia we realized that the adrenergic sympathetic reaction caused by intubation could not be suppressed by nalbuphine-HCl (NAL), a new narcotic agonist-antagonist in the same way as by fentanyl (FE). The aim of the study was to investigate whether the observed autonomic reaction could be overcome by: (a) varying the interval between injection of NAL and intubation or (b) increasing the induction-dose of NAL. MATERIALS and METHODS. After receiving institutional approval and the patients' written informed consent, a two-part randomized trial arrangement was made using two groups of 10 surgical patients each. During the first part the induction-dose of NAL was 1.5 mg/kg BW and that of FE was 0.005 mg/kg BW. Midazolam 0.15 mg/kg BW was the induction hypnotic. Orotracheal intubation was performed 15 min after NAL and 10 min after FE injection. During the second part, the NAL dosage was 2.5 mg/kg BW and intubation was carried out 10 min after opiate injection. Induction conditions in the FE group were unchanged. RESULTS. NAL causes adrenergic sympathetic hemodynamic and autonomic reactions immediately after injection (Figs. 1a + b, 2a + b). The rate-pressure product increase during intubation is significantly higher after NAL than after FE administration and cannot be suppressed by increasing the dosage or increasing the injection-intubation interval. In contrast, the postoperative period is characterized by long-lasting analgesia (114 min vs 82 min in the FE group) and sedation, especially after administration of 2.5 mg/kg BW NAL. CONCLUSION. These results may be explained by the agonist-antagonist activity of NAL at the opiate receptor sites.