BACKGROUND: Ropivacaine is an amino amide local anesthetic that has an advantage of a low-toxicity profile. Clonidine, an alpha2 adrenergic agonist, is known to prolong and intensify anesthesia from epidural local anesthetics. The aim of this study was to evaluate the dose-response effects of added clonidine to ropivacaine-fentanyl epidural anesthesia for lower extremity surgery. METHODS: Forty-five patients undergoing lower extremity surgery were randomly allocated to three groups to be given the following agents by an epidural route: 0.75% ropivacaine 15 ml+fentanyl 50microgram with clonidine 50microgram (group I), 100microgram (group II), or 150microgram (group III). Onset and maximal height of sensory block, and duration of sensory and motor block were assessed. Also, blood pressure, heart rate and sedation score were measured. RESULTS: Duration of sensory and motor block of groups II and III was significantly longer than that of group I, but there was no difference between group II and group III. Two segment regression times were significantly different among the three groups. Onset of sensory block, blood pressure, heart rate, and sedation scores were not significantly different among the three groups. CONCLUSIONS: The addition of Clonidine 100 and 150microgram prolonged duration of anesthesia more than 50microgram with ropivacaine-fentanyl epidural anesthesia for lower extremity surgery.