The stability of bile acid turnover rate was evaluated retrospectively using repeat SeHCAT tests in patients with chronic diarrhoea and prospectively for 16 years in healthy subjects. The SeHCAT values were stable in 39 patients with chronic diarrhoea, as shown by a comparison of the test results [data presented as median and (25th-75th percentile)]: 18% (8-23) in the first test versus 14% (9-21) in the second test [n = 39, P = 0.37, time interval 44 months (16-68), repeatability index >95%]. In contrast, they were reduced after 16 years in healthy subjects: 38% (30-49.5) in the first test versus 31% (21-49.5) in the second test (P < 0.03). In healthy subjects, the body mass index increased by 13% from 23.2 kg/m(2) (21-24.6) to 26.2 kg/m(2) (22.5-27.8) (P < 0.01) during the 16 years. There was a negative correlation between hepatic bile acid synthesis and the SeHCAT values (r = -0.615, P = 0.02, n = 14). In conclusion, the turnover rate of bile acids is stable over a long period of time in patients with chronic diarrhoea irrespective of bile acid malabsorption, suggesting that a repeat SeHCAT test is dispensable. There is a significant negative correlation between bile acid synthesis and SeHCAT test results in healthy subjects. The SeHCAT test values are slightly reduced in healthy subjects after 16 years.