Cereal fiber may reduce the risk of colorectal cancer by diluting colonic contents due to increased fecal output, by accelerating intestinal transit, by increasing fecal frequency and by altering bacterial metabolism. The effects of whole-meal rye bread on some putative colon cancer risk markers were investigated in 17 healthy Finnish subjects using a randomized crossover trial with two 4-wk bread consumption periods and a 4-wk washout period between the bread periods. White wheat bread was used as a control. Test breads covered a minimum of 20% of the daily energy intake (range, 4330-14, 033 kJ/d). Intestinal transit time, stool weight, fecal bacterial enzyme activities and short-chain fatty acid, ammonia, diacylglycerol (DAG) and bile acid concentrations in feces (expressed per gram wet feces) were measured. Whole-meal rye bread significantly increased fecal output and fecal frequency and shortened mean intestinal transit time compared with wheat bread in both women and men. Activities of beta-glucuronidase and beta-glucosidase (expressed per gram wet feces) were significantly lower in men and urease activity significantly higher in women during the rye bread period (RBP). Fecal butyrate concentration was higher during the RBP in men. Fecal ammonia and DAG concentrations did not differ between bread periods. Fecal total and secondary bile acid concentrations were significantly lower during RBP in both women and men. This study shows that whole-meal rye bread significantly improves bowel function in healthy adults and may decrease the concentration of some compounds that are putative colon cancer risk markers.