Results of arterial blood gas and acid-base analysis on initial samples prior to therapy were reviewed for 220 dogs admitted to the University of Georgia Veterinary Teaching Hospital. Acidemia or alkalemia was detected in 61 of 220 dogs (28%). The most common acid-base abnormality was metabolic acidosis (79 of 220 dogs--36%). Primary metabolic acidosis was the acid-base category associated most frequently with the combination of vomiting and diarrhea, dehydration, and the combination of polydipsia and polyuria, whereas normal mean arterial PCO2 and [HCO3-] values and primary metabolic acidosis were detected with equal frequency in vomiting, diarrhea, and cyanosis. Arterial hypoxemia was found most frequently in patients with restrictive respiratory tract disease (restricted lung expansion), lower respiratory tract disease, heartworm disease, and circulatory system disease. Significantly lower (P less than or equal to 0.05) arterial pH and PO2 were detected initially in dogs that eventually died, as compared with dogs that were improved at the time of discharge from the hospital. Mean [HCO3-] values also were lower initially in dogs that eventually died, as compared with those that improved, but the differences were not statistically significant.