Expression pattern of microRNA-155 (miR-155) in the serum of chronic genotype 4 (GT4)-hepatits C virus (HCV)-infected patients with different responses prior (naïve) and subsequent to treatment (end of treatment, EOT). The expression of miR-155, as represented in relative quantitation (RQ), was quantified in the serum of naïve and EOT GT4-HCV-infected patients classified into non-responders (NRs) and sustained virological responders (SVRs). Naïve NRs (n=10) showed a significant downregulation in miR-155 expression compared to the healthy controls (n=12) (**P=0.0025) and naïve SVRs (n=9) (*P=0.0280). EOT NRs (n=10) also showed a significant downregulation in miR-155 expression compared to the healthy controls (***P=0.0007) and EOT SVRs (n=10) (*P=0.0188). Naïve SVRs did not show any significant difference in miR-155 expression compared to the healthy controls (P=0.6196), whereas EOT SVRs showed a significant upregulation (*P=0.0234). Results are expressed as mean of relative quantitation ± standard error of the mean. ns, not significant.