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 13C or 14C has relative advantages and disadvantages. 13C-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 13CO2 analysis are large compared to those for 14CO2. The protocol details for use of the 13C-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 13C urea and new analytical techniques for the measurement of 13CO2 should allow reduction in the length of the test and its cost; they may herald a more widespread clinical application of this useful test.