Ethyl (Z)-(3-ethyl-4-oxo-5-piperidino-thiazolidin-2-ylidene)-acetate (piprozoline, Gö 919, Probilin) and its main metabolite Gö 3284 induce a strong choleretic effect in dogs after i.v. and i.d. administration as well. Intestinal absorption is fast, and already 3.5 min after administration of the substances a rise of the bile volume and of the optical density of the secreted bile can be observed. The secretion rates of bile solids and bile acids per time (min) increase almost at the same time, too. Moreover, piprozoline presumably stimulates the synthesis of bile acids and of the other matter in addition to the raised secretory rate. In the group of choleretics, piprozoline is to be placed among the cholepoietics. Under the influence of piprozoline and Gö 3284, the content of solids sometimes decreases for a short period immediately after administration of substances. A strong linear correlation occurs between the secretion rate of bilirubin and bile acids. The increase of bile volume under the influence of piprozoline and Gö 3284 may be seen as osmotic effects caused by the stimulation of the bile acid dependent and the bile acid independent (Na+-ion dependent) canalicular mechanisms of choleresis.