Arterial blood concentrations of lidocaine were measured in 7 patients undergoing pancreas operation during continuous epidural anesthesia and repeated doses of lidocaine were given according to the skin temperature of the toe. After the epidural catheter placement at the middle level of thoracic spine, 3 ml (test dose) plus 9 ml of 2% lidocaine with epinephrine (1:200,000) were injected. Additional doses of lidocaine, 6 ml, were injected when the skin temperature of the toe decreased for 0.3 degrees C. Two cases were excluded from this study because the skin temperature did not increase following additional doses of lidocaine. Lidocaine was added for 3.4 times on an average during anesthesia (duration 345 +/- 35 min, mean +/- SE). The first, second, third and fourth intervals of repeated injections from the initiation of epidural anesthesia were 119 +/- 10 min, 184 +/- 16 min, 251 +/- 20 min and 323 +/- 27 min, respectively. Arterial blood concentrations of lidocaine before each injection were 2.4 to 2.8 micrograms.ml-1 and these values showed no significant changes. These results demonstrate that the estimation of the necessity of additional injections by monitoring the skin temperature during prolonged epidural anesthesia prevents the lidocaine intoxication.