In a double-blind study, 42 children, aged 1-10, undergoing general subumbilical surgery, were randomly allocated to two groups; they received, via caudal extradural, 1% mepivacaine 7 mg.kg-1 and normal saline 1 ml (Group 1) and a mixture of 1% mepivacaine 7 mg.kg-1 plus clonidine 2 micrograms.kg-1 and normal saline up to 1 ml (Group 2) respectively. No significant difference was noticed in age, weight, duration of surgery and onset time of anaesthesia, blood pressure, heart rate and oxygen saturation. Mean duration of analgesia (evaluated with 'Broadman objective pain scale') was 143 min for Group 1 and 218 min for Group 2 (P < 0.05); the time of sedation (evaluated with a sedation score) was statistically longer in Group 2 (172 min vs 89 min in Group 1). This longer sedation is due both to the longer analgesia and partially to a side effect of clonidine. In conclusion the addition of 2 micrograms.kg-1 of clonidine to mepivacaine prolongs the duration of caudal analgesia in children.