Background: Ras oncogenes are found in 25% of human tumors and they significantly affect prognosis. One of the major fields studied to improve anticancer drugs is blockade of the oncogenic ras protein function. One of the mechanisms to block the function of these proteins is to block farnesylation using a farnesyl transferase inhibitor (FTI) and thus to prevent the ras from anchoring to the cell membrane. Methods: In this study, we investigated the effects of FTI L-744,832 either alone or in combination with 5-fluorouracil (5-FU; 1 mu M/l) and radiotherapy ( 2, 6, and 10 Gy) on the colon cancer cell line DLD-1 with mutations in K-, N- and H-ras, c-myb, c-myc, p53, fos, sis and DNA repair genes. Drugs were added 3 h after cultivation. Radiotherapy was performed on the 3rd day of the study. On the 3rd day, medium and drugs were changed. Evaluations were performed on the 6th day. Results: Administration of L-744,832, neither alone nor its combination with 5-FU and radiation, affected the number of DLD-1 cells and apoptosis rates. Regarding its effects on the cell cycle, L-744,832 was shown to lead to G(0)/G(1) and G(2)/M accumulation in a dose-dependent manner when administered alone. However, in combination with 5-FU, only a G(0)/G(1) accumulation was observed. Conclusion: Our study showed that FTI L-744,832 does not effect the cell number and apoptosis rate of DLD-1 cells and it cannot overcome 5-FU and radiation resistance, although it is able to modify some phases of the cell cycle. Copyright (C) 2005 S. Karger AG, Basel.