We have determined the effectiveness and degree of motor block produced by the new local anaesthetic, ropivacaine, when used for caudal anaesthesia in children. We studied 60 children, aged 3-6 yr, ASA I, allocated randomly in a double-blind manner, to receive one of two local anaesthetics: 0.375% ropivacaine 1.0 ml kg-1 or 0.375% bupivacaine 1.0 ml kg-1. Patients were anaesthetized with continuous infusion of propofol 200 micrograms kg-1 min-1. The lungs were ventilated with 50% nitrous oxide in oxygen. Heart rate and arterial pressure were measured every 5 min after administration of local anaesthetic until discharge from the recovery room. The extent of motor block in the recovery room was scored as 1-3. Adverse events and time to first analgesic requirements were recorded. Patients in the two groups did not differ in age, weight or height. There were no differences in heart rate or arterial pressure between the two groups. No adverse events were observed. The degree of motor block was significantly different between the two groups. The ropivacaine group showed a shorter duration of motor block than the bupivacaine group (P < 0.05). Postoperative analgesia was required at a mean time of 5 (SD 3.2) h in the ropivacaine group compared with 5 (2.8) h in the bupivacaine group. These findings suggest that caudal anaesthesia with ropivacaine in paediatric patients is effective and produces less motor block in the postoperative period.