The goal of this study was to investigate interrelationship between changes in anti-hepatitis C virus antibody and response to antiviral therapy. The comparative quantitative analysis of antibodies to individual structural and nonstructural viral proteins was done during two years in three patient groups: initial responders, non-responders and a reference group (without therapy). All patients in the treated groups exhibited decrease in the analyzed antibodies to HCV proteins, but with different patterns. The first statistically significant difference in the decrease of virus-specific antibody between initial responders and non-responders was observed within the first three months of therapy beginning. Some treated patients demonstrated decrease in antibody levels to HCV proteins after the end of therapy.