Besides type I interferons (IFNs), type III IFNs, including IFNλ1 (interleukin-29 [IL-29]), possess potent antiviral activity. In patients infected with the hepatitis C virus (HCV), it has been demonstrated that viral clearance is associated with genetic variation near the IFNλ3 (IL-28B) gene. The rapid influx of research being conducted on this family of cytokines has led to several inconsistencies and controversies, including the possible correlation of serum cytokine levels with disease in chronic viral hepatitis patients. In a detailed study, well-characterized cohorts of patients with HBV and HCV were evaluated with 3 different immunoassays, and no differences in the levels of serum IFNλ were observed between patient groups, disease stages, or clinical parameters.