Aspirin is widely prescribed and confers considerable benefit to patients by reducing cardiovascular and cerebrovascular morbidity and mortality. Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective analgesics, antipyretics and reduce the inflammatory component in conditions such as rheumatoid arthritis. However, both agents are associated with an increased risk of gastrointestinal symptoms and the potentially serious consequences of gastroduodenal ulceration, bleeding and perforation. The introduction of highly selective cyclo-oxygenase (COX)-2 inhibitors or the coprescription gastroprotective agents with nonselective NSAIDs have offered strategies to reduce the incidence of such events. This review article analyzes the quantitative techniques that can be employed by clinical pharmacologists and the clinical studies performed to assess NSAID damage in the gastrointestinal tract.