Aberrant crypts are putative preneoplastic lesions that have been proposed as intermediate biomarkers for colon cancer. The goals of these studies were to determine (i) if the colon cancer chemopreventive agent, sodium phytate, when started 1 week after a single dose of carcinogen, has any effect on the development of aberrant crypt foci (ACF) in treated rats; and (ii) if ACF at an early time period under these conditions correlate with the later formation of tumors in similarly treated animals. The number of ACF with four or more crypts was greater (P = 0.02, Mann-Whitney test) in rats with tumors compared with rats without tumors killed at 36 weeks after the injection of azoxymethane (AOM); the total number of ACF was not significantly different in these two groups. The incidence of tumors in F344 rats treated with AOM without phytate was 83% (10/12) compared to 25% (3/12) in rats treated with AOM plus phytate (P = 0.0045, two-tail Fisher's exact test). The finding of more (P = 0.005, Mann-Whitney test) ACF with four or more crypts in rats without phytate than in rats with phytate at 12 weeks after the injection of AOM is consistent with the hypothesis that the development of larger ACF (with four or more crypts) is predictive of the tumor incidence. These results validate the use of this parameter, i.e. ACF with four or more crypts, as an intermediate biomarker for tumor incidence in this system.