Erosive duodenitis is a clinical entity whose pathogenesis is still obscure. Acid secretion is mostly normal, while the possible role of vascular factors has been suggested. We measured mucosal blood flow by means of laser Doppler velocimetry during endoscopy in the duodenal bulb of 10 subjects with erosive duodenitis, 10 duodenal ulcer patients, and 10 healthy controls. Duodenal blood flow in erosive duodenitis was significantly reduced (p < 0.001) compared with controls, whereas no changes were detected in duodenal ulcer. Reassessment of mucosal blood flow after a 6-week treatment with ranitidine failed to show any increase in the perfusion values even in patients with endoscopic healing. Our results suggest that impaired mucosal blood flow is a primary factor in the pathogenesis of chronic duodenal erosions.