Boar spermatozoa were diluted in Ringer’s fructose or sulfate buffer and incubated aerobically for 4 hr at 37 C (a) in the presence of potassium hydroxide (KOH), hyamine hydroxide, or diethanolamine (DEA) absorbents, and (b) in 1, 2, or 3% atmospheric levels of carbon dioxide. Oxygen uptake by boar spermatozoa was enhanced by the presence of DEA compared with KOH and hyamine hydroxide. Incubation with DEA resulted in increased spermatozoan livability, more desirable cell motion, and smaller increases in buffer pH. Oxygen uptake by boar spermatozoa was optimum with 1 or 2% carbon dioxide, depending upon which buffer cells were diluted in. Levels of 2 and 3% carbon dioxide maintained oxygen uptake and livability of boar spermatozoa during later stages of the incubation period equally as well as 1% carbon dioxide. As the level of atmospheric carbon dioxide increased, buffer pH remained closer to the initial value.