The relationship between faecal bacteria, faecal bile acids and transit time was investigated in nine patients with cholerrheic enteropathy and ten normal subjects. In five of the patients and five normal subjects bacteriological examination of the faeces indicated that qualitatively and quantitatively the flora was similar. The bile acid concentration in the majority of patients was higher (p < 0.001) than in normals and was in the range found to inhibit 7α-dehydroxylation in a parallel in vitro study. Transit time only affected 7α-dehydroxylation when the concentration of bile acids was less than 15 mM