The usefulness of culturing gastric biopsies obtained by endoscopic visualization, Gram stain, immediate and late urease test, and histologic observation of Campylobacter pylori in the diagnosis of gastric mucosa infection by Campylobacter pylori was assessed in 75 patients. Four antral biopsies were obtained in 75 patients, 35 with duodenal ulcer and 40 with nonulcerous dyspepsia and all specimens were subjected to the above procedures. Positive criteria for infection were either a positive culture or the concurrence of positive Gram stain, positive urease test before 24 hours and observation of the Campylobacter pylori at the histologic preparations. The sensitivity and specificity of every test was calculated. The most useful tests were the biopsy culture and the early urease reaction. It should be pointed out that the ureasa test is rapidly done, has a low cost, and possess a high degree of reliability. Therefore it is very useful to the clinician and to the endoscopist.