To evaluate the sensitivity and specificity of assays used to screen blood for antibody to hepatitis C virus (HCV) infection, the International Consortium for Blood Safety (ICBS) established fully characterized ICBS panels. ICBS collected and characterized 1007 anti-HCV-positive plasma units from geographically diverse origins by ELISA, RIBA, RT-PCR, and sequence-based genotyping, 539 of which met the definition of a true positive. Of these, 200 confirmed positive plasma units, representing the 6 major HCV genotypes, were selected to assemble the true-positive constituents of the panel. The negative panel comprises 181 plasma units collected from the USA. The panels have proved valuable for determining the performance of anti-HCV assays thus permitting national authorities, especially in resource-limited countries, to make informed decisions on selection of affordable and reliable assays.