Cell proliferation was studied in descending, transverse and ascending colonic crypts of rats fed either 0%, 0.6%, 1.2% or 2.0% phytic acid (PA). Significant effects of phytic acid were seen only in the descending colon. No changes in crypt height were observed. Both the 1.2 and 2.0% phytic acid groups exhibited significantly lower uppermost labelled cells than the control group. Animals given 1.2% and 2.0% phytic acid also showed significantly reduced DNA synthetic cells, as indicated by lower labelling indices.