The predictive value of cystatin C as a marker of course of the disease has been evaluated. Fifty-two pairs of serum samples of patients with B non-Hodgkin lymphoma have been collected at the time of diagnosis and before fourth cycle of chemotherapy. The levels of cystatin C, CRP, β
2M, LDH, and IL-6 in samples have been measured, and clinical parameters of course of the disease (B symptoms, clinical stage, patients' age, and IPI) have been noted. In total patient's group cystatin C levels correlated with β
2M and IPI. In aggressive lymphomas, the inhibitor levels correlated with clinical stage of disease and were significantly higher in patients with elevated LDH activity. In aggressive nodal lymphomas its levels correlated with β
2M, IPI, and clinical stage of disease. The cystatin C level was significantly increased in total group of patients over 60 years old, while in particular types of lymphoma, no statistical significance has been obtained. Our results indicate that cystatin C should be taken into consideration in disease monitoring. However, we expect that the disease-free and overall survival analysis will give the definitive answer about the reliability of cystatin C as an indicator of course of aggressive lymphomas.