The urea breath test (UBT) is generally considered as a simple, non-invasive and accurate test to demonstrate Helicobacter pylori (H. pylori) infection. The principle of the test is simple. The orally given urea, isotopically labelled with 14C or 13C, is hydrolysed by the enzyme urease of H. pylori and *CO2 is expired in breath. Although the radiation exposure is negligible (3*10(-6) Sv), the test with the stable isotope 13C should be preferred. Since the first description of the test in 1987 many refinements have been described. Most studies reported sensitivity and specificity figures between 95-100% for both. A uniform test protocol with regard to the test meal, the appropriate 13C-urea dose, the number of breath samples to be taken, ... would be ideal. But today, it is better to strive for a validation and a determination of cut off values for each protocol as such. The main indication for UBT is the confirmation of successful eradication. To avoid false negative results, testing should be performed 4 to 6 weeks after the end of treatment and 5 days after the end of acid suppressive drugs. The test is also an ideal tool to check for infection when an ulcer is found at endoscopy, but biopsy specimens can't be taken because of anticoagulant treatment. Mostly serology is the first choice to perform epidemiological studies, but UBT is a good alternative and moreover it gives an idea of the presence of active infection. The role of non-invasive tests, i.e. UBT and serology, in primary diagnosis of H. pylori is more controversial. Questions such as who will perform the test (general practitioner or gastroenterologist), what is the age limit, how to organise the follow up, what is the cost-benefit, ... still remain. All these questions need a further evaluation in terms of its influence upon clinical decision making not only in general, but also more specific for the Belgian situation.

In conclusion: 1. The 13C-urea breath test is a very accurate, non-invasive test to diagnose gastric H. pylori colonisation in adults and children. 2. If local protocols are validated and appropriate cut off values are determined, general standardisation of methodology isn't necessary. 3. The 13C-urea breath test is the ideal diagnostic tool to monitor eradication therapy in patients with complicated duodenal ulcers, gastric ulcers, Malt lymphomas, poor compliance and to perform large epidemiological studies. 4. The role of the 13C-urea breath test in the clinical decision making prior endoscopy remains controversial.