In acute experiments with anesthetized dogs, the intravenous injection of medium and large doses of glucagon produced a triple modification in pancreatic juice secretion. The secretion rate was first transiently augmented, then was distinctly and persistently depressed, then finally returned to control values. The initial acceleration in secretion corresponded to the greatly increased arteriovenous blood sugar differences produced by the glucagon. The subsequent depression in secretion usually began while the A-V differences were still elevated. Return of secretion to control values coincided with return of A-V blood sugar differences to control values.