The present study was designed to investigate the modifying effects of dietary exposure to NaCl and four kinds of crude salts on the induction and development of aberrant crypt foci in Fischer 344 rats. A total of 57 male rats were divided into five groups at six weeks of age, and all were given weekly injections of azoxymethane (15 mg/kg body wt s.c.) for three weeks. Group 1 was fed a normal diet throughout the experiment as control group. Groups 2, 3, 4, and 5 were fed diets containing 4.4% pure NaCl, 4.4% cooking salt, 4.4% rock salt, and 4.4% beach salt, respectively, from one week before the first azoxymethane dosing. The mean numbers of aberrant crypt foci and aberrant crypts per colon were significantly lower in Groups 3-5 than in Group 1 (p < 0.01). The present results suggest that the other mineral components (e.g., calcium and magnesium) of these crude salts, rather than pure NaCl, may be chemopreventive agents for colonic tumorigenesis.