1. Forty-eight male rats were fed sequentially for 14 d periods on diets containing different fibre contents.
2. One of the high-fibre diets was a commercial pelleted diet. The other was a low-fibre diet supplemented with 200 g wheat bran/kg.
3. At the end of each feeding period eight rats were killed. Liver microsomal cholesterol 7α-hydroxylase (EC 1.14.1.-) activity and bile acid content of small intestine and colon were determined.
4. The different diets did not significantly alter the total intestinal bile acids, but affected the distribution and qualitative pattern in the colon and small intestine.
5. On the high-fibre diets deoxycholate, and hyodeoxycholate tended to be increased.
6. On the low-fibre diets the α-, β- and ω-muricholic acids tended to be increased.
7. Liver microsomal cholesterol 7α-hydroxylase activity was lower in rats fed on the low-fibre and bran- supplemented low-fibre diets compared with that in rats fed on the commercial pelleted diet.