Studies performed in the author's laboratory concerning the role of gastric mucosal blood flow in ethanol-induced gastric mucosal injury and prostaglandin cytoprotection are reviewed. Fluorescent in vivo microscopic and hydrogen gas clearance studies revealed total absence of blood flow in the gross ethanol-induced lesions. Prostaglandin pretreatment not only prevented gross lesion formation but flow was present throughout the mucosa. A cytoprotective dose of the prostaglandin analogue did not increase blood flow. Transmitted light in vivo microscopy revealed rapid cessation of blood flow through mucosal microvessels within 1 min of ethanol application. The microvessels remained filled with red blood cells, suggesting an intravascular coagulation phenomenon. Histologic studies revealed no necrotic lesion formation 1 min after ethanol, but increasing necrosis from 10 to 60 min. These findings suggest that the rapid ethanol-induced cessation of blood flow renders the gastric mucosa more susceptible to ethanol injury and prostaglandin acts by preventing this blood flow change.