For some time we have been much concerned with the highly discussed question of the mechanism of evacuation of the gallbladder. A consideration of the results obtained by Boyden, Whitaker, Higgins and Mann, Burget and others,1from such procedures as the feeding of egg yolk and fat, and the effect of transfusion of the blood of fed animals on the emptying of the gallbladder, led us directly to the conviction that the effect of intravenous administration of "secretin" preparations must be thoroughly studied. With this objective in mind, we have performed several series of experiments, the results of which prove to be exceptionally significant. METHODS AND RESULTS It was necessary, before such a study could be initiated, to prepare highly purified preparations of "secretin." This has been done by Ivy, Kloster and Lueth2starting with the preparation of Weaver, Luckhardt and Koch.3Responses of the pancreas have