Esherichia coli endotoxin was administered intravenously to 7 Holstein adult cows, to evaluate the effect of endotoxin on acid-base balance. Endotoxin shock was observed immediately after the administration of endotoxin. A loss of appetite and depression of digestive tract motility continued for about 120 hr after the challenge. Metabolic alkalosis following hypochloremia and hypokalemia were particularly pronounced at 12 to 72 hr after the administration of endotoxin.