Summary The respiratory function of the blood of prairie dogs (Cynomys ludovicianus ludovicianus (Ord)) has been studied. The position of the oxygen dissociation curve is to the left of other rodents closely related to this species and of similar size. The prairie dog blood resembles in some respects small mammals found at high altitudes and in other respects animals living near sea level. This is considered an adaptation to the habits and habitat of the species. Appreciation is expressed to Mr. Ronald Barbee for technical assistance.