The effect of ketamine on the duration of atracurium-induced neuromuscular blockade was studied in 40 healthy patients anaesthetized with midazolam, fentanyl and nitrous oxide. Twenty received, in addition, i.v. ketamine 2 mg kg-1 followed by an infusion of 2 mg kg-1 h-1. Atracurium 0.5 mg kg-1 was injected i.v. and the time to 25% recovery of the twitch height was measured. It was 8.0 min longer in the ketamine group (P less than 0.005), with a 95% confidence interval of from 2.3 to 11.8 min.