The influence of carbon dioxide absorbent on the respiration and motility of boar spermatozoa in vitrowas studied in 18 trials using whole semen. Three collections were obtained from each of six Yorkshire boars, and aliquots of each collection were divided into two treatment groups. Potassium hydroxide was used to absorb the released carbon dioxide in group one, and diethanolamine was used in group two.During the 3-hr, incubation period at 37° C, pH increased from 7.65 to 9.20 in group one and from 7.6S to 8.40 in group two. This was accompanied by a decrease in motility from 84.5 to 2.1% in group one and from 84.5 to 32.9% in group two. Total oxygen consumption (µl./1O8sperm) during the 3-hr, incubation period was 32.4 µl. for group one and 57.2 µl. for group two. All differences between the two treatment groups were highly significant.Diethanolamine significantly reduced the loss of bicarbonate from boar seminal plasma which occurred when using potassium hydroxide as the carbon dioxide absorbent. The difference between the two treatment groups in loss of bicarbonate resulted in a significant difference in final pH. This in turn was responsible for the significant differences in final motility and total oxygen consumption between the two treatment groups.