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. We conducted this study measuring the phagocytic activity of blood platelets. 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. The study demonstrated that embolization led to an increase in platelet count and decrease of phagocytic index.