Changes occur in the electrolyte pattern of the blood serum of the dog following exercise on the inclined treadmill. Although the lactate conc. may continue to rise and bicarbonate to fall for some mins., the fall in bicarbonate exceeds the rise in lactate. With comparable high lactate concs. after both a 2-min. and a 25 to 37 min. run, recovery is more rapid after the shorter run. Phosphate and K fall markedly in conc. for some time but return to the initial level within 2 hrs. Chloride often continues to rise for at least 10 mins. and remains elevated, while protein falls rapidly after exercise.