Patients with long-standing ulcerative colitis (UC) have an increased risk for developing colorectal cancer (CRC) compared to the general population. For investigation of the mechanisms and prevention of UC and UC-related CRC, establishment of a promising animal model for such disease is important. 1-hydroxyanthraquinone (1-HAQ) present in certain medicinal plants such as Rubia tinctorum L. is a genotoxic and rodent colon carcinogen. Long-term feeding of 1-HAQ induced hyper-cell proliferation in rat colonic crypts with ulcerative changes, crypt abscess, severe inflammation and erosion before the occurrence of tumors, which are similar to those found in human UC. In addition, 1-HAQ has a synergistic effect with methylazoxymethaol (MAM) acetate on colon carcinogenesis. The polymerase chain reaction-single strand conformation polymorphism analysis revealed no mutations in Ki-ras and p53 in colonic neoplasms induced by MAM acetate + 1-HAQ, MAM acetate alone or 1-HAQ alone. Also, no mutations of APC were found in these tumors. These findings are similar to those found in human ulcerative colitis-associated colon cancer in contrast with sporadic colon cancers. A previous study revealed that induced colonic tumors had beta-catenin mutation with high frequency, suggesting tumor development by activation of the beta-catenin-Tcf signaling pathway. Increased expression in TNF-alpha and IL-1alpha was found in these induced colonic neoplasms, and the expression was more remarkable in colonic mucosa of rats exposed to MAM acetate + 1-HAQ, MAM acetate or 1-HAQ when compared with that in untreated rats. Thus, these cytokines may act as growth factors in rat colon carcinogenesis by MAM acetate and 1-HAQ and the synergistic effect of 1-HAQ with MAM acetate might be related to the biological effects of the cytokines expressed in the inflammatory conditions induced by 1-HAQ.