UNLABELLED Colon cancer morbidity in Poland is still increasing. During the course of the disease thromboembolic complications are often observed. It was documented that components of the hemostatic system influence cancer progression. The presence of coagulation factors was revealed in colon cancer tissue. So far the information on the presence of inhibitors of coagulation in this tumor type was lacking. The aim of the study was to evaluate the expression of coagulation inhibitors in loco in colon cancer. MATERIAL AND METHODS Immunohistochemical method employing polyclonal antibodies directed against tissue factor pathway inhibitor (TFPI), antithrombin III (AT Ill), protein C (PC) and protein S (PS) was introduced. RESULTS The presence of TFPI was observed in cancer cells in a part of examined specimens, but the intensity of the staining was different. In most cases of colon cancer AT III expression of low intensity was revealed in a few cancer foci. In approximately 15% of cases there was no AT Ill expression, while in other 15% of examined fragments of colon cancer AT Ill was readily detected. Weak expression of TM was observed in most colon cancer tissues, but only in some cancer foci. In 1/3 of examined cases the strong expression of TM was revealed. Weak and heterogeneous intensity of expression of PC was demonstrated in about 75% of colon cancer cases, whereas in about 25% of the specimens--the expression of this protein was strong. Furthermore in most cases there was no or weak expression of PS. Only in about 25% of the cases the staining for PS was strong. Expression of TFPI, AT III and PC was revealed in macrophages, whereas TFPI and AT Ill were detected in mucus in the lumen of neoplastic glands, and TM--in endothelial cells. CONCLUSIONS Weak representation or the lack of coagulation inhibitors in colon cancer in most cases may facilitate coagulation activation in the tumor burden, and consequently promote colon cancer progression. Heterogeneous and inconstant presence of blood coagulation inhibitors in colon cancer in loco may suggest, that nonocoagulant biological activities of these inhibitors may influence the cancer growth or its inhibition in an individual patient. Obtained results suggest that introducing various forms of blood coagulation inhibitors in the treatment of colon cancer patients may be beneficial in selected group of patients.