The effect of ketamine on the onset time, the duration of action and the recovery characteristics of suxamethonium-induced neuromuscular blockade was examined in a double-blind randomized study comprising 30 patients anaesthetized with thiopentone, fentanyl, midazolam and nitrous oxide. The ulnar nerve was stimulated at the wrist using train-of-four stimulation (TOF; 0.2-ms duration, 2-Hz frequency every 10s), and the evoked twitch response was measured with a force-displacement transducer. After stabilization of the twitch recording, the patients in the ketamine group received ketamine 2 mg kg-1 i.v., followed by a ketamine infusion of 2 mg kg-1 h-1. The remaining patients served as controls and received equivalent volumes of isotonic saline. Suxamethonium I mg kg-1 was injected 2 min after the ketamine/placebo bolus dose. The onset time, recovery index, time to 90% recovery of the twitch height and the TOF ratio during recovery were similar in the two groups. Therefore, it is concluded that ketamine does not affect suxamethonium-induced neuromuscular blockade in man.