Induction of apoptosis is an attractive strategy in cancer therapy but it clinical practice is not yet sufficient in choriocarcinoma. The quinolinone derivative, vesnarinone, is a novel inotropic agent used for treating congestive heart failure and may also have a potential anticancer activity. It induces apoptosis and differentiation in some tumor cell lines. We examined the antitumor effect of vesnarinone in eight cell lines established from human choriocarcinoma and hydatidiform mole using MTT assay and also analyzed the nuclear fragmentation of tumor cells by DNA electrophoresis assay. Vesnarinone inhibited the proliferation of choriocarcinoma cell lines in a dose-dependent manner and induced DNA fragmentation in cells. However, the BM cell line prepared by subcultivation from hydatidiform mole showed no growth suppression or DNA fragmentation in response to vesnarinone. On the other hand, PCR-SSCP analysis and direct DNA sequencing have shown that a human choriocarcinoma cell line, SCH, has a mutant p53 gene at codon 249. When SCH cells were treated with vesnarinone cellular proliferation was significantly inhibited. Vesnarinone suppressed the proliferation of all choriocarcinoma cell lines and induced apoptosis, regardless of the existence of p53 mutation. In addition, it has been found by RT-PCR that expression of c-Myc mRNA is upregulated by treating choriocarcinoma cells with vesnarinone. The finding suggests that vesnarinone might induce expression of c-Myc gene in choriocarcinoma cells, the product of which may be associated with the inhibition of cell growth and induce apoptosis. These results suggest that vesnarinone is a useful reagent for the treatment of choriocarcinoma.