Two hundred and ten patients were defined as having dyspepsia of unknown origin. At endoscopy 11% had body gastritis, 46% antral gastritis, and 19% bulbitis (two thirds combined with antral gastritis). Histologically, 22% had chronic corpus gastritis (79% superficial, 21% atrophic), which was combined with chronic antral gastritis in 84%, 33% had chronic antral gastritis (82% superficial, 18% atrophic); and 14% had duodenitis, which was combined with antral gastritis in 65%. Polymorphonuclear leukocytes were found in specimens from the body mucosa in 6%, from the antral mucosa in 13%, and from the duodenal cap in 4%. The endoscopic findings correlated significantly with the histologic findings in the duodenal bulb (kappa = 0.33) but not in the stomach. The frequency of endoscopic antral gastritis and the frequency of histologic chronic body and antral gastritis increased with age. Endoscopic bulbitis and histologic duodenitis and gastric metaplasia were commoner in men than in women. Peak acid output was higher in patients with than in those without endoscopic bulbitis and higher in smokers than in non-smokers when the significant sex differences in peak acid output were taken into account. Gastric metaplasia of the bulb was predominantly correlated to higher peak acid output and to some extent also to sex and smoking. Episodic pain was correlated to histologic duodenitis. Other dyspeptic symptoms and the intragastric bile acid concentration were not associated with any endoscopic or histologic findings. Of the 210 patients, 172 were reexamined after a double-blind 6-week treatment period with cimetidine, antacid, or placebo. The symptomatic outcome of these treatments was not associated with any significant change in endoscopic or histologic findings.