Our aim was to investigate if interferon plus ribavirin has any effect on serum HCV quasispecies distribution and the relationship between diversity of HCV quasispecies and treatment response. In all, 21 patients were treated with interferon plus ribavirin for 48 weeks. The presence of HCV quasispecies was determined in serum samples at baseline and at the fourth week of treatment by SSCP analysis of the hypervariable region. SSCP pattern was defined as single or multiple band. A single band was found in six patients and multiple bands in nine. No significant difference was found between SSCP pattern in pretreatment samples and response to the therapy. In none of the patients were observed changes in number of SSCP bands between samples taken at baseline and in the fourth week of the therapy. In conclusion, the complexity of HCV quasispecies before the therapy was not related to treatment response; combined therapy did not affect serum HCV quasispecies.