Some recent studies of the effects of chemopreventive agents have begun to use new rodent models to improve the analysis of stages of colonic preneoplasia, and how chemopreventive agents modify progressive abnormal cell development. In one of the models of inherited predisposition to colon cancer, mice carrying a truncated Apc allele with a nonsense mutation in exon 15 have been generated by gene targeting and embryonic stem cell technology (Apc1638 mice). These mice develop multiple gastrointestinal lesions, including adenomas and carcinomas, focal areas of high-grade dysplasia (FAD), and polypoid hyperplasias with FADS. The incidence of inherited colonic neoplasms has now been modulated by a chemopreventive regimen. Colonic lesions significantly increased in Apc1638 mice on a Western-style diet, which has higher fat content and lower calcium and vitamin D compared to the same mice on AIN-76A diet. In another rodent model, Min mice were treated with sulindac, which markedly reduced the incidence of intestinal tumors. A third new rodent model containing a targeted mutation in the gene Mcc (mutated in colorectal cancer) recently became available for chemoprevention studies. These mice develop multiple types of neoplasms including adenocarcinomas, focal areas of gastrointestinal dysplasia, papillomas of the forestomach, and tumors in other organs including lung, liver, and lymphoid tissue. Feeding a Western-style diet to the Mcc mutant mice also resulted in significantly increased gastrointestinal lesions. These nutrient modifications also have been given to normal mice, demonstrating without any chemical carcinogen that a Western-style diet induced colonic tumorigenesis. Western-style diets also have now induced modulation of cell proliferation in other organs including mammary gland, pancreas, and prostate. These findings help develop new preclinical rodent models to aid the analysis of genetic and environmental factors leading to neoplasia, as well as new methods for evaluating the chemopreventive efficacy of specific nutrients and pharmacological agents.