Blood gas values corrected for temperature were compared to uncorrected values in 35 cases of open heart surgery and the following results were obtained. 1) The corrected pH values were higher than the uncorrected values, and a 1 degrees C decrease in the rectal temperatures resulted in an increase pH values by 0.013(Y=-0.013x + 0.504, p<0.01). 2) The corrected values for PCO2 were lower han the uncorrected values, and a 1 degrees C decrease in the rectal temperature resulted in a decrease in corrected PCO2 values by 1.256mmHg(Y=-1.256x + 49.267, p<0.01). 3) The corrected values for PO2 were slightly lower than the uncorrected values, and the differences between temperature corrected and uncorrected PO2 values had statistically significant, but clinically no significant correlation (Y=-3.236x + 133.075, p<0.01). 4) The differences between temperature corrected and uncorrected base excess values had no satistical correlation. 5) If the uncorrected pH values were maintained around 7.4 at any temperature then the corrected pH values at each temperature were very close to the theoretically ideal values (Y=-0.014x).