Thirty-six adult patients who received caudal anesthesia for perianal surgery were rando-mly agsigned to two grgups. Of these, 15 patients ingroup 1 were given 1.5 and 2% plain lidocaine in 18 and 7 ml doses, repectively. Twenty-one patients in group 2 were given lidooaine carbonated with 5% NaHCO3 0.1 ml per 1 ml-lidocaine in the same volume and concentration as in group 1. The time of onset of analgesia for the pin prick and scratch tests was significantly more rapid in group 2(2.04+/-0.63 and 4,69+/-1.12 min for the pin prick and scratch tests, respecti-vely-) than those in group 1(5.00+/-1.70 and 9.48+/-5.40 min for the pin prick and scratch test, respectively). However, the duration of anesthesia in both groups was not significantly different (111.80 +/-40.24 and 105.95+/-45.04 min in group 1 and 2, respectively). The mean pH of the 1.5 and 2% agents used in group 1 was 5.289+/-0.206 and 5.257+/-0.193, respectively, while the mean PH of the 1.5 and 2% carbonated lidocaine used in group 2 was 7.004+/-0.079 and 7.023+/-0.288, reapectively. The results iridicate that pH-adjusted lidocaine for caudal anesthesia has a more rapid onset than plain lidocaine hut that there is no difference in the length of duration of its effect.