Bambuterol is an inactive prodrug which is enzymatically cleaved by plasma cholinesterase to yield the active compound, terbutaline. This catalytic process is accompanied by a selective inhibition of plasma-cholinesterase, the enzyme also necessary for the break-down of succinylcholine. We therefore studied the possible effect of bambuterol on succinylcholine-induced neuromuscular blockade in a double-blind fashion in patients undergoing surgery under general anaesthesia. Of the 39 patients studied, 13 patients had 10 mg of bambuterol, 12 had 20 mg and 14 were given placebo 10-16 h prior to anaesthesia. Succinylcholine 1 mg.kg-1 bw was administered after induction of anaesthesia. Following supramaximal train-of-four stimulation of the ulnar nerve, the tension developed in the adductor pollicis muscle was measured. Onset time and the durations of action (times to 10%, 25%, 75% and 90% recovery of the first twitch of the train-of four response) were recorded. The mean recovery times were prolonged 30-50% in patients who had received 10 or 20 mg of bambuterol as compared with placebo. It is concluded that a prolonged duration of action of succinylcholine can be expected in patients being treated with bambuterol.