The dose-response curves of vecuronium and pancuronium were compared during ketamine anaesthesia in 60 patients (ASA I). The relationship between the probit transformed depression of twitch height and the logarithm of the dose was analysed by linear regression. Vecuronium was found to be 1.2 times more potent than pancuronium. ED50 of vecuronium and pancuronium were 30.5 microgram kg-1 and 37.0 microgram kg-1, and the ED95 45.6 microgram kg-1 and 59.5 microgram kg-1, respectively. Using equipotent doses of vecuronium and pancuronium (1.6 ED95) indices of neuromuscular blockade were compared in a further 20 patients (ASA I). No statistically significant difference was found in onset time. The duration of action following vecuronium was significantly shorter than after pancuronium. The time to 25% recovery of twitch height following vecuronium 73 microgram kg-1 was 22.2 min compared with 66.6 min following pancuronium 99 microgram kg-1. Following supplementary doses of vecuronium, a statistically significant increase in duration of action was seen following the fourth and fifth doses. Reversal time of vecuronium to a train-of-four ratio of 0.7 was significantly shorter than that of pancuronium (8.3 min and 13.6 min, respectively).