The Mayo Clinic experience with more than 200 bile acid breath tests was analyzed retrospectively to assess its clinical value. In patients with suspected bacterial overgrowth, the result of the bile acid breath test was compared with that of culture of aspirates of small bowel, and the test was found to have a sensitivity of 0.70 and a specificity of 0.90 (1.0 highest possible value). Although in one-third of the patients with a positive small-bowel culture the bile acid breath test failed to demonstrate the presence of bacterial overgrowth, analysis of the data according to the Bayes theorem showed that, compared with a routine evaluation without a small-bowel culture, the availability of breath test results will double the probability with which the clinician can be certain about the presence or absence of bacterial overgrowth. The test result appeared to influence the diagnosis in 83% and the management in 74% of the 163 patients in whom it was performed because of suspected bacterial overgrowth. In patients with suspected malabsorption of bile acids, on the other hand, the test that was performed without determination of fecal bile acid excretion appeared to be rather insensitive, and only rarely was information gained that was not already known from a routine workup of the patient.