BACKGROUND: Atracurium is eliminated by Hofmann elimination and ester hydrolysis, with minimal renal and hepatic excretion. It's action duration is not affected by renal function. Although metabolism of vecuronium is less dependent on the renal function than other steroid type neuromuscular blockers, the action duration of vecuronium is prolonged in renal failure. The purpose of this study is to compare the differences of the action duration of atracurium and vecuronium in patients with renal failure. METHODS: Forty patients with normal renal function and 40 patients with chronic renal failure were assigned to one of four groups: atracurium-normal (n=20, AC group), atracurium-renal failure (n=20, AK group), vecuronium-normal (n=20, VC group), vecuronium-renal failure (n=20, VK group). Anesthesia was induced with thiopental and maintained with the inhalation of nitrous oxide (50%) and isoflurane (0.5~1.5 vol%). Atracurium (0.5 mg/kg) or vecuronium (0.1 mg/kg) was given and endotracheal intubation was performed after twitch response was depressed more than 80%. Neuromuscular blockade was assessed by train-of-four at the adductor pollicis with supramaximal stimulation of ulnar nerve of 2 Hz every 12 sec. The onset time, duration of 5, 25, 50, 75% recovery time and recovery index were checked. RESULTS: Onset of block was not significantly different among four gorups. Recovery time of 5, 25, 50, 75% and recovery index were longer in the both renal failure groups. Action durations in renal failure were not significantly different between AK and VK groups. CONCLUSION: It is concluded that action duration of atracurium and vecuronium are affected by renal function. We would better monitor muscle relaxation and titrate dose of muscle relaxant.