In this study, the chemiluminescence (CL) of peripheral blood polymorphonuclear leukocytes (PMNLs) and the serum total antioxidative system (TAS) were assessed in patients with chronic C hepatitis (CCH) before and after 3 and 6 months of treatment with interferon (IFN)- and thymus factor X (TFX). The study included 26 patients with CCH aged between 25?63 years (mean: 42.67). Combined therapy with IFN-alpha 2a and a TFX preparation was applied. PMNL metabolic activity was assessed applying the whole-blood CL method. We measured CL response of neutrophils unstimulated and stimulated by opsonized zymosan, N-formyl-methionyl-leucyl-phenylalanine (N-fMLP), and phorbol-myristate-acetate (PMA) without and after priming with tumor necrosis factor alpha (10 ng/ml). The assessment of serum TAS was performed directly before the beginning of therapy with IFN-alpha and TFX and after 3 and 6 months of the treatment. A colorimetric method based on the reduction of the cationic radical ABTS+ (cation 2, 2'-azido-bis-[3-ethylobenzothiazolino-6-sulfonate]) in the presence of serum antioxidants was used. As a result of the treatment with IFN-alpha and TFX, the formation of free oxygen radicals by resting (unprimed) neutrophils increased statistically significantly both without stimulation and following stimulation by fMLP and PMA. A statistically significant increase in the serum antioxidant capacity was observed, which suggests the induction of compensatory processes. Increased in vitro reactive oxygen species production by both stimulated and unstimulated peripheral blood neutrophils of patients with CCH was observed. Treatment with IFN-alpha and TFX resulted in a compensatory increase in serum antioxidative capacity.