Chronic gastroduodenal ulceration is the end product of an imbalance between acid levels, peptic hostile factors, and mucosal defenses. This condition differs significantly from stress ulceration, in which the primary factor is decreased mucosal blood flow, and from nonsteroidal anti-inflammatory drug-induced injury, in which there is local vascular injury and inhibition of prostaglandin synthesis. The identification of H pylori as a cause of chronic gastritis, duodenitis, and peptic ulcer is required for specific antibacterial therapy.