The incidence of infections increases during treatment with pegylated interferon (PEG-IFN) and ribavirin (RBV) for chronic hepatitis C (CHC). Despite a reduction in neutrophil count, there is no clear relationship between infection occurrence and neutropenia. In the present study we investigated whether HCV treatment alters leukocyte function. We studied cell chemotaxis, reactive oxygen species, neutrophil phagocytosis, CR3 expression, and plasma colony stimulating factors (CSF) in 20 healthy subjects and 20 patients with CHC (10 with cirrhosis) at baseline, during antiviral treatment (at 4, 12, 24 weeks), and 12 weeks after discontinuation. Our results demonstrate that neutrophil chemotaxis and oxidative burst significantly increased during treatment and returned to baseline at the end of therapy. CR3 neutrophil expression was enhanced in baseline CHC compared to controls but did not change during antiviral treatment. Chemotaxis, oxidative burst, phagocytosis, and CSF levels did not differ significantly between patients before treatment and control subjects or among CHC cases according to the presence of cirrhosis in either cell subpopulation. In conclusion, the innate immune cell activity is enhanced in patients with CHC during antiviral treatment and returns to normal after its discontinuation thus possibly playing a role in their susceptibility to infections.