Vesnarinone, a quinolinone derivative, induces apoptosis and differentiation in some tumor cell lines. We examined the antitumor effect of vesnarinone on three human hepatocellular carcinoma (HCC) cell lines. Vesnarinone suppressed the proliferation of all three HCC cell lines, but did not induce apoptosis and differentiation. Vesnarinone has also been reported to inhibit both nucleoside and nucleobase transport. Concomitant administration of vesnarinone and a de novo nucleotide synthesis inhibitor potentiated the growth-inhibitory effect of vesnarinone on HCC cells. Vesnarinone may be useful as a new biochemical modulator of anticancer agents.