The study was conducted to determine whether four bile acids (CA, cholic acid; DCA, deoxycholic acid; CDCA, chenodeoxycholic acid; LCA, lithocholic acid) affects the development of aberrant crypt foci (ACF), a putative preneoplastic lesions of colon, after administration of azoxymethane (AOM). Male F344 rats received two injections of AOM (15 mg/kg) at an interval of 7 days starting from 5 weeks of age. They were fed either basal diet (MF) or MF plus 0.4% bile acid for eight weeks started from first shot of AOM in 5 rats/group. The numbers of ACF/colon of the rats fed CA, DCA, CDCA and LCA were 293+/-69, 266+/-73, 332+/-94 and 251+/-25, respectively, while that of basal diet-fed case was 130+/-18. The number of ACF was significantly higher in all the rats fed bile acid (p<0.01). No significant increase of the number of ACF by these four bile acids without AOM was encountered compared to the basal diet control.