115 general and urologic surgery adult patients, ASA class I–II, were divided in four groups according to initial bolus and relaxant used : group A atracurium 0.6 mg · kg −1, group B 0.5 mg · kg −1, group C vecuronium 0.1 mg · kg −1 and group D pancuronium 0.1 mg · kg −1. When the single twitch recovered to 25 % of control height (T 25), subgroups were individualized depending on whether repeat doses of 1/3 of initial bolus were given or not, and whether reversal was spontaneous or obtained by a standard dose of neostigmine 2.5 mg and atropine 1.25 mg. By ulnar nerve stimulation at the wrist, the force of thumb adduction was recorded on a polygraph; single twitch (tw), train of four (tof) and ratio tof 4/1 (Rtof) were measured. Anaesthesia was induced with thiopentone and fentanyl without premedication and maintained with fentanyl and N 2O in oxygen; the trachea was intubated once the block was at its maximum. The onset time of maximal block was 5 min for groups A, B and C, and 7.9 min for group D. T 25 was 39.9 ± 8.5 min for group A, 34.4 ± 9.7 min for group B, 28.9 ± 9.9 min for group C and 70.7 ± 25.9 min for group D. A Rtof equal to 75 % was achieved in less than 65 min with atracurium and vecuronium, but much later with pancuronium. Reversal at T 25 was efficient, but not really required, for atracurium and vecuronium, but necessary and useful for pancuronium. The recovery index and duration of action of pancuronium were two or three times longer than for vecuronium and atracurium. No cumulative effect was observed after two or three repeat doses in groups A, B and C; duration of action of vecuronium increased with age. These two non-depolarizing relaxants, devoid of haemodynamic effects, could not replace suxamethonium for urgent intubation but were easier to use than pancuronium. Because of its metabolism, atracurium seemed preferable in older patients or in patients with renal or hepatic failure, whereas vecuronium should be kept for use in atopic patients because the former releases histamine.