Embolization consists in the occlusion of renal artery and its ramifications, which induces acute renal infarction. Renal artery embolization, causing necrosis, stimulates cellular reactions within and around the neoplasm. The interaction of neoplastic cells with blood platelets is of great importance in the development of neoplastic disease. Neoplastic cells exert a stimulatory effect on blood platelets. During activation, platelets change in shape and secrete certain substances. The aim of the present study was to evaluate morphological parameters of blood platelets in renal cancer patients before and after renal artery embolization. 45 patients suffering from renal cancer were examined (22 women and 23 men) before and after embolization. Diagnosis was established basing on the patients' history, clinical picture, and ultrasonographic, urographic and angiographic examinations. Tumour advancement was defined as T2 and T3. The study has demonstrated that embolization leads to an increase in platelet count and in the percentage of "megathrombocytes". The changes observed in the study may indirectly testify to the involvement of the thrombopoietic system in the course of neoplastic disease.