Pentoxifylline (PTX), a methylxanthine derivative, is commonly used in patients suffering from peripheral vascular diseases. Besides its well-known hemorheological properties PTX has been found to decrease the secretion of some inflammatory cytokines such as TNF, IL-12 and IFN-gamma. PTX also suppresses lymphocyte cytotoxicity, affecting mainly the perforin-dependent pathway. We investigated the influence of PTX on the splenocyte cytotoxicity and leukocyte infiltration in a murine colon adenocarcinoma model. We observed that PTX decreased the cytotoxic activity of isolated splenocytes against C-26 cells and reduced the inflammatory cell infiltration in the peritumoral tissue. Thus, our results strongly suggest the necessity of further studies concerning the safety of PTX use, especially in elderly patients or patients with already diagnosed cancer.