Hyperventilation of patients during surgical anesthesia is a common practice in the United States. The results obtained in the present study re-emphasize serum potassium concentration is directly proportional to arterial carbon dioxide tension, and that for every 10 torr decrease in PaCO2 there is a concomitant 0.5 mEq/L decrease in potassium. Therefore sudden and significant levels of hypokalemia may occur during the course of a general anesthetic, and since hypokalemia is known to be capable of producing serious cardiac arrhythmias, hyperventilation should be avoided during surgical anesthesia, particularly in patients on drugs which produce electrophysiologic changes similar to those resulting from hypokalemia.