The aim of the study was to determine the effect of renal tumor embolization on nonspecific immunity by evaluating lysozyme activity and leucocytosis in 45 patients and 40 healthy people. Lysozyme activity was assessed in the non-diluted serum (A1) and in the tenfold diluted serum (B1) prior to embolization and after embolization (A2, B2) and in control group. Prior to embolization, lysozyme activity was lower in the experimental group (A1 and B1), compared to the control groups, the differences being statistically significant (p < 0.05). After embolization, the activity became normalized (A2), reaching the control value and even exceeding it (C) in the diluted serum (B2). Leucocytosis prior to embolization (L1) resembled that of control group, increasing slightly after embolization (L2). The differences observed in the changes in lysozyme activity and leucocytosis were statistically significant (p < 0.05). Our findings indicate an inhibitory effect of the neoplastic process on nonspecific immunity. Embolization causes ischemic necrosis of tumor and products of neoplastic tissue disintegration exert a stimulating effect on granulopoiesis, by increasing the turnover of neutrophilic granulocytes. Granulocytic-monocytic infiltrations in tumor stroma are the source of lysozyme, enhancing not only local but also systemic immunity, which is manifested in the increased lysozyme activity in blood serum.