The urea breath test (UBT) is the most sensitive and specific non-invasive test for the detection of Helicobacter pylori infection both before and after treatment, Labelling of the urea with either C-13 or C-14 has relative advantages and disadvantages. C-13-UBTs are both safe and well-validated, and have the additional advantage that they can be used in children. However, the initial capital costs of (CO2)-C-13 analysis are large compared to those for (CO2)-C-14. The protocol details for use of the C-13-UBT are variable: a test meal is important if urea solution is to be used and a single sample time point at 30 min is adequate. The recent development of novel formulations of C-13 urea and new analytical techniques for the measurement of (CO2)-C-13 should allow reduction in the length of the test and its cost; they may herald a more widespread clinical application of this useful test.