Farnesyltransferase inhibitors, butyrate and butyric acid derivatives have previously been reported to exert anti-tumor activity in experimental models in vitro and in vivo and have recently gained acceptance as potential anticancer agents. In our study, we examined antitumor effects of a combination of a farnesyltransferase inhibitor L-744,832 and butyrate in vitro against MDA-MB-231 and MIA PaCa-2 human cancer cells. This combination therapy showed synergistic antitumor activity against MDA-MB-231 cells, which was at least in part due to induction of p27KIP1 expression. Both drugs increased intracellular levels of p53 as well but there was no significant difference between the groups treated with single drugs and the group treated with their combination. In MIA PaCa-2 cells, the combination therapy exerted additive antitumor activity. Our results illustrate possible application of the farnesyltransferase inhibitor L-744,832 and butyrate as a combination therapy of cancer.