The purpose of this study was to compare the time course of action and tracheal intubating conditions of vecuronium, rocuronium and mivacurium in anaesthetised patients. Anaesthesia consisted of thiopentone, fentanyl, N2O/O2 and isoflurane. After a 2 x ED90 dose the first attempt at tracheal intubation was made at 90 s. If required, maintenance doses of 0.5 x ED90 were administered. The intubating conditions after rocuronium were significantly better than those after vecuronium and mivacurium. The average onset times of rocuronium (172 s) and vecuronium (192 s) were significantly shorter than that of mivacurium (229 s). The clinical duration and recovery time were significantly shorter after mivacurium (13 and 6 min, respectively) than with vecuronium (33 and 14 min, respectively) and rocuronium (28 and 11 min, respectively). We conclude that rocuronium might be of advantage whenever the interval between the administration of the muscle relaxant and tracheal intubation must be short, whereas mivacurium may be of benefit if fast spontaneous recovery is required.