The microvasculature of the gallbladder, the common bile duct, and the duodenal papilla was investigated in 20 albino guinea pigs (Cavia porcellus) using microvascular corrosion casting and scanning electron microscopy (SEM). Main supplying and draining vessels (first-order vessels) approach the gallbladder along the cystic duct. From the latter, penetrating vessels (second-order vessels) arise which pierce the muscular coat of the gallbladder body to form the plexus of third-order vessels between the muscle coat and the mucosa. Third-order vessels finally branch to supply the subepithelial capillaries, which show a honeycomb arrangement, corresponding to the gallbladder pits. At the areas bordering mucosal pits and beneath the tunicae plicae mucosae, the capillaries form glomera. These structures make the mucosal vasculature suitable for adapting to gallbladder wall distension caused by volume changes. The mucosal capillary glomera may also be involved in absorption of substances from bile, or they could act as buffer zones, counteracting the pressure which develops as the gallbladder volume increases. Venous sphincters occurring at the junction of mucosal vessels with the subjacent third-order veins may regulate blood flow in the mucosal glomera. The neck region as well as bile ducts consist of 2 vascular layers: an inner capillary layer and an outer one containing arterioles and venules. The duodenal papilla has a hemispheric shape and is interposed in the transition zone between the stomach and the duodenum. On the most luminal aspect, the capillaries of the papilla have a ring-shaped arrangement, as do the capillaries of the stomach, surrounding the mucosal glands; the remainder of the papilla is covered by duodenal villi capillaries.