BACKGROUND The purpose of this study was to examine pharmacodynamics, pharmacokinetics and safety of Org 9426 (rocuronium bromide) in Japanese patients. METHODS Seventy-eight patients anesthetized with thiopental, droperidol, fentanyl and nitrous oxide, were randomized to receive either a single dose of Org 9426 0.3 mg x kg(-1), 0.6 mg x kg(-1) or 0.9 mg x kg(-1). Contraction of the adductor pollicis to the ulnar nerve stimulation (0.1 Hz) was measured by acceleromyography. Blood was sampled over 6 hr and pharmacokinetic variables were calculated by plasma concentrations of Org 9426. RESULTS Onset times for patients receiving 0.3 mg x kg(-1), 0.6 mg x kg(-1) or 0.9 mg x kg(-1) were 271.5 s, 140.0s and 125.4s, respectively. There was a dose-dependent increase in clinical durations until 25% recovery of twitch height (17.4 min in 0.3 mg x kg(-1) group, 37.2 min in 0.6 mg x kg(-1) and 60.4 min in 0.9 mg x kg(-1) group). Pharmacokinetic study revealed that elimination half life, steady state volume of distribution and plasma clearance of Org 9426 were 48-76 min, 146-181 ml x kg(-1), and 3.8-4.5 ml x min(-1) x kg(-1), respectively. No adverse effects were found except a case of local erythema on a forearm. CONCLUSIONS The efficacy of neuromuscular block, stable pharmacokinetic behavior and excellent safety of Org 9426 were also confirmed in Japanese surgical patients.