Capnometer has been used in anesthesia for the evaluation of pulmonary ventilation because of its nonivasive and continuous monitoring advantges. We studied pulmonary ventilation effects with arterial blood gas parameter between normoventilation and hyperventilation with capnometric control during 1 hr duration. We devided two group. Control group was maintained PetCO2 38 mmHg and experimental group PetCO2 28 mmHg and four times arterial blood gas sample were done. The results were as follows. 1) Serum K+ concentration was decreased siginifcantly in hyperventilation group. 2) Arterial pH changes were observed respiratory alkalosis in experimental group and respiratory acidosis in control group. 3) (a-t)PCO2 differnce were increased in both group and especially control group with correlation of time duration. 4) No arrhythmia were detected in both group. We conclude that only capnometric control of pulmonary ventilation is not suffieient and it has to be combined periodic ABGS and resetting of ventilation mode.