The circulatory pattern in the gastric mucosa of the rat and relationships of mucosal capillaries to gastric gland cells were investigated. Techniques used included the vascular corrosion cast/scanning electron microscope method, scanning electron microscopy of acid-digested tissues, conventional transmission electron microscopy and in vivo light microscopy. Arterial break-up into capillaries invariably occurs around the base of the gastric glands. The mucosal capillaries are fenestrated and vesiculated, and pass in close proximity to the abluminal aspects of the cells of the gastric glands, particularly the parietal cells. At the apices of the glands, the capillaries form a honeycomb network closely applied to the abluminal aspect of the surface epithelial cells, before draining into infrequent venules which are embedded in a substantial connective tissue sheath. No capillary drainage occurs into these venules deeper in the mucosa. No evidence of either mucosal or submucosal arteriovenous anastomoses was found. Because of the close proximity of the fenestrated mucosal capillaries to the parietal cells and surface epithelial cells and the direction of capillary blood flow, the alkaline tide of the actively secreting parietal cell must be transferred to the abluminal aspect of the surface epithelial cells. The capacity of these cells to secrete HCO3- or to neutralize back diffusing H+ ions would thereby be increased.