The purpose of this study was to examine whether crude á-mangostin (a major xanthone derivative in mangosteen pericarp (Garcinia mangostana)) has short-term chemopreventive effects on putative preneoplastic lesions involved in rat colon carcinogenesis. The crude preparation was obtained by simple recrystallization of an ethylacetate extract of mangosteen pericarps. A total of 33 five-week-old male F344 rats were randomly divided into 5 experimental groups. Rats in groups 1-3 were given a subcutaneous injection of 1,2-dimethylhydrazine (DMH)(40 mg/kg body weight) once a week for 2 weeks. Starting one week before the first injection of DMH, rats in groups 2 and 3 were fed a diet containing 0.02% and 0.05% crude á-mangostin, respectively, for 5 weeks. Rats in group 4 also received the diet containing 0.05% crude á-mangostin, while rats in group 5 served as untreated controls. The experiment was terminated 5 weeks after the start. Dietary administration of crude á-mangostin at both doses significantly inhibited the induction and/or development of aberrant crypt foci (ACF) (P<0.05 for 0.02% crude á-mangostin, P<0.01 for 0.05% crude á-mangostin), when compared to the DMH-treated group (group 1). Moreover, treatment of rats with 0.05% crude á-mangostin significantly decreased dysplastic foci (DF) (P<0.05) and â-catenin accumulated crypts (BCAC) (P<0.05), to below the group 1 values. The proliferating cell nuclear antigen (PCNA) labeling indices of colon epithelium and focal lesions in groups 2 and 3 were also significantly lower than in group 1 and this effect occurred in a dose dependent manner of the crude á-mangostin. This finding that crude á-mangostin has potent chemopreventive effects in our short-term colon carcinogenesis bioassay system suggests that longer exposure might result in suppression of tumor development.