It is common to check arterial blood gas values during anesthesia to know the state of acid-base balance and tissue oxygenation, but there are many complications in performing arterial puncture or cannulation. The purpose of this study is to know the correlations of blood gas values between arterial and venous blood freom the hand during balanced anesthesia. Twenty five patients of both sexes were investigated. The values of pH, pCO2, pO2, B.E., B.B., and HCO2(-) of arterial and venous blood were compared graphically and regression equations were made. All the measurements except pO2 showed close correlation.