In 110 patients with unknown Helicobacter pylori status and without anti-bacterial treatment submitted for routine endoscopy of the upper gastrointestinal tract biopsies were taken from the antral and body mucosa, which were assessed for H. pylori colonisation and/or gastritis by an urease test (Jatrox H. p.-Test), microscopy after methylene-blue staining of a mucosal smear, specific culture and histology (stains: haematoxylin & eosin and Warthin-Starry). In addition, a simplified 13C-urea breath test was validated. A complete set of data was available from 104 patients (64 women - 40 men, median of age: 55 years [range: 17-92 years], H. pylori positive histologically and/or culturally [goldstandard]: n = 67). The test criteria sensitivity, specificity, positive and negative predictive value were calculated to be 100%/100%/100%/100% for the urease test, 76.1%/100%/100%/69.8% for microscopy of a mucosal smear, and 92.5%/97.3%/98.4%/88.1% for 13C-urea breath test (two-point measurement). Statistical analysis demonstrated highly significant (p < 0.0001) correlations between the reaction velocity of the urease test, the histologically visible degree of Helicobacter pylori colonisation and the differences of the delta-values of the 13C-urea breath test on the one hand and between grade and activity of gastritis as well as between the gastritis and activity scores, respectively, and the semi-quantitatively categorized results of the urease test, the histological degree of H. pylori colonisation and the 13C-urea breath test on the other hand.(ABSTRACT TRUNCATED AT 250 WORDS)