Editor,—We read with great interest the paper by McColl and colleagues (Gut1997;40:302–6) reporting the usefulness of the non-invasive Helicobacter pylori ¹⁴C-urea breath test (¹⁴C-UBT) in predicting underlying ulcer disease in patients with dyspepsia. By administering 0.4 MBq ¹⁴C-urea after the test meal, the cut off values calculated by the authors at 20 minutes seem to be very high—namely, above 40 kg% dose/mmol CO₂ for H pylori positive and less than 20 kg% dose/mmol CO₂for H pylori negative patients. The values between 20 to 40 are suggested to be equivocal. The authors have not given the basis for obtaining these cut off values. We have used the¹⁴C-UBT routinely since 1990 and so far have performed this test on almost 500 patients using a wide variety of test protocols. Based on our initial data, the cut off value for H pylori positive patients was calculated to be above 0.6% dose/mmol CO₂ × kg (body weight) 15 minutes after oral administration of 185 kBq ¹⁴C-urea without giving a test meal or cold substrate.1 Similarly, a theoretical value of 0.585% can be obtained at 15 minutes by multiplying the body weight of an …