The plasma concentrations of lidocaine were measured by HPLC(high-performance liquid-chromatography) when 415 mg of 1.5 and 2% plain lidocaine(group 1), carbonated lidocaine(group 2) and lidocaine with epinephrine(group 3) were injected into the caudal spaces of 30 patients. Peak concentrations were achieved 15, 20 and 30 min, after injection in group 1,2 and 3, respectively. The maximum values of mean concentration in group 1,2 and 3 were 3.30±0.83, 3.31±0.81 and 1.86±0.52 ug/ml (mean±SD), respectively. The plasma concentration in group 3 were lower than those in groups 1 and 2 at intervals of 5,10,15 and 20 min. However, it was uncertain whether carbonated lidocaine was absorbed more rapidly thus producing significantly higher blood concentrations. The results indicated a significant difference in the plasma concentration of epinephrine-mixed lidocaine from that of plain or carbonated lidocaine. We suggest that in caudal anesthesia, epinephrine(1:200,000) with lidocaine has an advantage with respect to lowering the plasma concentration of lidocaine.