The effect of dietary fiber type (cellulose, pectin, or oat bran) on colonic short-chain fatty acids (SCFA), luminal pH, and epithelial cell proliferation was examined in 60 male Sprague-Dawley rats. In vivo cell proliferation was measured by [3H]thymidine incorporation into DNA, pH was measured in vivo, and luminal SCFA were determined by gas chromatography. The pectin and oat bran diets produced higher concentrations of all types of SCFA and total SCFA than cellulose at every site. The higher the SCFA concentration, the lower was the pH at each site. In the cecum, the concentration of SCFA was positively associated with the number of cells per crypt column (r = 0.961), total cells per crypt (r = 0.963), and the proliferative zone (r = 0.845). In contrast, in the distal colon, there was no significant correlation between SCFA concentration and measurements of cell proliferation. These data suggest that fiber stimulates cecal cell proliferation through the production of SCFA. The effects of fiber on distal colonic cytokinetics are likely mediated through a different mechanism.