Ursodeoxycholic acid (UDCA) and lithocholic acid (LCA), secondary bile acid, have been shown to have a cell differentiation activity in the mouse F9 teratocarcinoma stem cells. treatment with the bile acids induced morphological changes, including cytoplasmic and nuclear membrane blebbing, aggregation of organelles, and chromatin condensation, corresponding to apoptosis. Moreover, the bile acids induced internucleosomal DNA fragmentation, a hallmark of apoptosis, assessed by gel electrophoresis. In addition, the bile acids increased the expression of c-jun, but decreased the expression of c-myc and laminin in F9 cells. These results suggest that the bile acids can induce apoptosis in F9 cells. Furthermore, the c-jun activation may be necessary for the apoptosis induced by LCA or UDCA in F9 cells.