OBJECTIVES: in elderly people, bacterial overgrowth of the small bowel may be occult. The significance of positive breath tests are uncertain: many fit elderly subjects with positive tests show no evidence of malabsorption. We assessed the prevalence and significance of bacterial overgrowth in the small bowel in a relatively unselected elderly population. METHODS: residents of seven elderly people's homes had a glucose hydrogen breath test. A medical history and anthropomorphic measurements were recorded. Volunteers with positive breath tests were given doxycycline. After 4 months all volunteers were reassessed. RESULTS: of 140 residents, 62 were tested. Nine (14.5%) had a positive breath test. There was no difference in anthropomorphic and bowel habit data between those with positive and those with negative breath tests. After 4 months of antibiotic treatment, volunteers with a positive breath test had increased weight and body mass index, while those with a negative test had decreased weight and body mass index. CONCLUSIONS: the percentage of volunteers with a positive breath test was much lower than in previous studies. This may be due to the relatively unselected nature of the volunteers. Treatment of bacterial overgrowth resulted in a small but significant improvement in anthropometric indices. The lack of association of positive breath tests with baseline anthropomorphic measurements or bowel habit highlights the occult nature of the bacterial overgrowth and questions its clinical importance.