The effect of increasing partial pressure of carbon dioxide (pCO2) on fructose disappearance, lactate accumulation, and CO2 evolution from bicarbonate, after correction for retention, of bovine spermatozoa was studied. In a diluent composed primarily of the sodium salts of citrate and bicarbonate, the metabolism was maximum with a gas phase of N2 and decreased with each increase in pCO2 to a minimum, about 10% of that under N2, with a pCO2 of 100%. The inhibition was reversible upon aeration of the sperm cells. After inhibition under 100% CO2 for 24 hours, the recovery of glycolytic function under 5% CO2, 95% N2 was nearly complete during an additional 4-hour period. In the sodium diluent all the hexose which disappeared was recovered as lactate. However, when the sodium was replaced by potassium, hexose disappearance was inhibited only slightly by CO2 and very little of the hexose was converted to lactate. Hexose disappearance was depressed by sulfanilamide at low pCO2 and acid end-products other than lactic may be formed.