BACKGROUND: Action of mivacurium varies in condition with reduced plasma cholinesterase activity. The aim of this study is to evaluate the pharmacodynamics of mivacurium and to obtain the infusion rate of mivacurium in patients with liver cirrhosis or cholestasis. METHOD: We allocated into three groups. Healthy subjects without hepatobiliary disease(Group I, n=10), patients with liver cirrhosis(Group II, n=5), and patients with cholestasis(Group III, n=9) received 5 mg/kg thiopental sodium and 1~2g/kg fentanyl. They were ventilated by mask with 2.5~3% enflurane(in O2/N2O 50%) until I/E ratio of enfurane concentration gt; or = 0.8, and then received 3 ED95 mivacurium(0.18 mg/kg). Accelerographic responses to train-of-four(TOF) stimulation of ulnar nerve at 15 seconds interval were used for neuromuscular monitoring. The onset time, the duration, recovery indices and infusion rate of mivacurium were compared among groups. RESULT: The durations from the injection of mivacurium to 10% single twitch recovered (Dur10) in group II(16.5+/-4.3 min) and III(17.1+/-0.6 min) were longer significantly than that in group I(10.7+/-5.3 min). The infusion rates to maintain a steady twitch height at 5~10% for 20 min in group II(1.9+/-1.5 microgram/kg/min) and III(1.6+/-0.7g/kg/min) were lower than that in group I(3.5+/-1.3 g/kg/min). However, there was no significant difference between group II and III. CONCLUSION: Clinical duration of relaxation with 3 ED95 mivacurium is prolonged significantly and infusion rate to maintain the steady twitch height at 5~10% is lower in patient with liver cirrhosis or cholestasis than in patient without hepatobiliary disease.