The 14CO2- glycylcholate breath test (also called the bile acid breath test) was performed in a group of 42 normal young volunteers (group A), a group of 25 elderly subjects in apparently good health (group B) and a group of 22 hospitalized geriatric patients presenting with weight loss (group C). The 95 percentile value of the cumulative 14CO2 excretion at the third and the sixth hour in group A was taken as the limit for normal values for 14CO2 excretion. Using these criteria 56% of group B subjects and 50% of group C patients were considered abnormal at the third hour, whereas at the sixth hour these percentages were 56% and 54%, respectively. Repetition of the bile acid breath test after antibiotic treatment in the hospitalized group suggested that bacterial overgrowth in the small intestine was responsible for the abnormal 14CO2 breath test in the elderly persons. However, the large number of abnormal tests in healthy elderly people, not complaining of any gastro-intestinal discomfort, indicates that bacterial overgrowth may remain asymptomatic and that an abnormal test does not necessarily mean that the symptoms of a patient are to be ascribed to this finding.