Aim. To evaluate the value of cytokeratin-18 fragments (CKF-18) for diagnostics of non-alcohol fatty liver disease (NAFLD): liver steatosis (LS) and steatohepatitis (SH). Material and methods. We examined 148 patients with NAFLD (94 men, 49 women) including 28 (19.6%) with LS and 115 (80.4%) with SH (mean age 48.85±10.36 and 48.6±12.0 years respectively). The diagnosis was verified based on clinical, ultrasonic, and liver biopsy (in 17 (12.0%) patients) data. CKF-18 were measured by the immunoenzyme assay (TPS ELISA,Biotech, Sweden) and TNF-alpha with the use of a Human TNFα Platinum ELISA kit (Bioscience, Austria). Control group consisted of 27 healthy donors. Results. CKF-18 level in SG patients (420.5±426.9 U/l) was significantly higher than in LS patients and healthy subjects (126.13±48.0 and 129.27±59.78 U/l respectively). TNF-alpha levels were 6.28±0.5, 5.15±0.6, and 4.81±0.7 pg/ml respectively (p<0,05). Correlation of CKF-18 levels with the following parameters was documented : ALT (r=+0,45, p<0,05); AST (r=+0,43, p<0,05), triglycerides (r=+0,25, p<0,05), HDLP (r=-0,21, p<0,05), histological activity index (r=+0,46, p<0,05). No correlation was found between CKF-18 and TNF-alpha levels or between CKF-18 and severity of fibrosis. Conclusion. CKF-18 levels in SH patients are significantly higher than in LF patients and correlate with histological signs of SH activity. Measurement of TNF-alpha can be used for differential diagnostics of SH and LF. Significant elevation of aminotransferase activities and CKF-18 levels in SH compared with LF and their close correlation confirms the important role of necrosis and hepatocyte apoptosis in pathogenesis of NAFLD.