BACKGROUND: The advantages of addition of epinephrine to local anesthetics during caudal epidural anesthesia are core intense block, prolonged duration of anesthesia and reduction of systemic toxic effect of local anesthetics. The currently recommended concentration of epinephrine is 1 : 200,000, but absorbed epinephrines cause unwanted hemodynamic changes, so we attempted to ascertain the minimum effective concentrations of epinephrine during caudal epidural anesthesia. METHODS: Ninty patients classified ASA physical status I or II scheduled for perianal surgery were studied. These patients were divided into four groups who received 20 ml of 2% lidocaine with epinephrine concentrations of 1 : 100,000, 1 : 200,000, 1 : 400,000 or 1 : 800,000 respectively. Before and during anesthesia, patients' mean arterial pressure (MAP) and heart rate (HR) were measured. Caudal anesthesia was performed with patients in the jack-knife position. A 3 ml test dose was administered initially and then the remaining local anesthetics were injected slowly. The onset of analgesia, duration of analgesia, and other complications were observed. RESULTS: The onset of analgesia was slowest in the 1 : 800,000 group. The duration of analgesia was longest in the 1 : 100,000 group. There were no significant difference in MAP changes, but HR increased significantly in the 1 : 100,000 group compared to the 1 : 200,00 group. There were no systemic toxic symptoms for local anesthetics except that 1 patient, who was in the 1 : 100,000 group, had symptoms of palpitation and headache, considered to be the unwanted pharmacologic effects of epinephrine. CONCLUSION: We concluded that the 1 : 400,000 epinephrine concentration can be used during caudal epidural anesthesia.