In this preliminary study, two groups of 15 patients, aged 1-4 years and 5-10 years respectively, received one of four doses of rocuronium (0.12, 0.17, 0.22 or 0.27 mg kg-1) and when block was maximal a supplementary dose to bring them all to a total of 0.5 mg kg-1. In half the patients, the block was reversed with atropine and neostigmine at a T1 recovery of 25%. The remainder were allowed to recover spontaneously. The total dose produced a block of 95-100% in all patients. The clinical duration of action was shorter under halothane anaesthesia in children (mean 15 min approximately) than has previously been reported in adults under intravenous anesthesia. Mean spontaneous recovery time from T1 25% to a train-of-four ratio of 0.7 was about 11 min. Neostigmine doubled the rate of recovery. There was a moderate increase in heart rate in the younger age range.