Helicobacter pylori has been implicated as an agent in the pathogenesis of antral gastritis, gastric and duodenal ulcer and probably in gastric cancer. The C13 urea breath test is a diagnostic method quick to perform, sensitive, reliable and non invasive. It is based on the presence of Helicobacter pylori urease activity, which permits to detect it in the infected mucosa. A substrate (urea) labelled with Carbon 13 is administered to the patient and exhaled breath is collected to detect the possible catabolism product (CO2 labelled with C13). In the European protocol, patients in fasting condition are given a test meal to delay gastric emptying and five minutes later a solution which contents 100 mg of C13 labelled urea. Breath samples are collected before and 30 minutes after urea was given. In our first year of experience, 363 patients with Helicobacter pylori infection detected by histology or urease were studied by C13 urea breath test, with a sensitivity and specificity of 95 and 96%. False negatives may occur if the test is used after antibiotics and other antiulcer drugs. Its main indication is to monitor eradication therapy after treatment. Its possible use as a quantitative test still remains unclear.