Since ribavirin has been proposed to modulate the host’s T cell responses, we studied its direct effects on CD4+ T cell clones with diverse functional polarization which had been generated from patients with chronic hepatitis C. We analysed in vitro proliferation ([3H] thymidine uptake) and cytokine responses (IL-10, IFN-gamma) at varying concentrations of ribavirin (0–10μg/ml) in 8, 9 and 7 CD4+ TH1, TH2 and regulatory T cell (Treg) clones, respectively. Here, IL10 is linked to chronic hepatitis C virus infection.