In order to investigate the pharmacokinetics of lidocaine especially the lung uptake during epidural anesthesia, we measured the lidocaine concentrations of arterial and central venous blood simultaneously using a homogeneous enzyme immunoassay. Then the lung extraction ratio was calculated as (1-arterial lidocaine concentration/central venous lidocaine concentration) X 100%. With only epidural anesthesia, the lung uptake of lidocaine was above 30% during the first 40 minutes, but was less after additional administration. After general anesthesia with thiamylal, enflurane, nitrous oxide and oxygen, the lung uptake was 30 approximately 40% following initial and additional administrations. There was a positive correlation between the lung extraction ratio and the central venous lidocaine concentration 5 minutes after the initial administration. Having used laryngotracheal lidocaine spray during endotracheal intubation, the lung extraction ratio could not be calculated since this resulted in direct lidocaine administration to the lungs. In conclusion, the lung plays an important role in keeping the arterial lidocaine concentration low.