Abstract: To optimize the .sup.14 C-urea breath test for Helicobacter pylori (a) a collection method for alveolar breath samples, (b) varying the post-dosage breath collection time and (c) varying the concentrations of KOH in the liquid trap employed for the capture of .sup.14 CO.sub.2 are employed. Collection of alveolar breath samples in bags was convenient for user and patient. The test provided optimal sensitivity and specificity for the detection of H. pylori infection when breath collections were performed 10 min after dosage with .sup.14 C-urea, and when breath CO.sub.2 was captured in liquid traps containing 80 or 800 mM KOH.