Studies in normal volunteers from our laboratory and by other investigators have demonstrated that non-steroidal anti-inflammatory agents (NSAIDs) can significantly damage the gastroduodenal mucosa. This damage is maximal with plain and buffered aspirin products. The injury produced by non-aspirin NSAIDs in anti-inflammatory doses is less than with aspirin but depends primarily on the dosages used. Pro-drugs and enteric-coated aspirin tend to produce less injury. The incidence of gastric ulcer in 1064 normal volunteers studied in our laboratory over a period of 7 years is reviewed. Seventy-two (6.7%) normal subjects developed a gastric ulcer after 7 days of therapy with anti-inflammatory doses of these drugs. The largest number of ulcers were seen with plain and buffered aspirin, and the lowest number with the lower anti-inflammatory doses of the non-aspirin NSAIDs.