The effect of bile acid perfusion on colonic motor function in vitro has been studied. It was found that bile acid perfusion and carbachol perfusion had no effect on the frequency or incidence of slow wave activity. However, the secondary bile acid deoxycholic acid (15 mmol/l) was shown to cause a statistically significant increase in percentage motility of the isolated colon (control 24.2 + 5.5%, deoxycholic acid 64.9 + 7.3%, p less than 0.01). The magnitude of this increase was similar to the increased colonic motility recorded during carbachol (2.5 micrograms/cm3) infusion. Chenodeoxycholic and cholic acids did not increase colonic motility in vitro.