The belief that blood flow plays a central role in cytoprotection and there being no data available, at present, regarding the possible action of Colloidal bismuth subcitrate (CBS-DENOL) on the gastric mucosal blood flow (GMBF), led us to investigate its influence on mucosal hemodynamics in the rat stomach. Measurements of GMBF were performed in 32 male Wistar rats, treated by either CBS or placebo in drinking water for a 3-wk period, by the use of a laser-Doppler flowmeter, at 14 defined points of the stomach. CBS treated animals revealed a highly statistically significant increase (P less than 0.0005, upaired t-test) of GMBF in comparison with the placebo treated. These findings lead us to suggest that CBS exerts its antiulcer action via the mechanism of increased gastric mucosal blood flow. Additionally the increased blood flow may be associated with the previous findings of increased synthesis of prostaglandins, gastric mucus and bicarbonate secretion by CBS.