Pérez-García A, et al. - In this prospective study carried out at a regional reference hospital in Spain, a total of 303 samples from 124 people were examined in order to assess the ability of HCV core antigen (HCV-cAg) as a marker of active HCV infection in newly diagnosed individuals, for treatment monitoring, and for the discovery of therapeutic failure. An excellent relationship between HCV-cAg and HCV-RNA was observed. Most diverging outcomes were noted in the treatment follow-up group. Thus, as a marker for active HCV infection, new diagnosis, the discovery of the antiviral therapeutic failure, and treatment monitoring, HCV-cAg showed superior sensitivity and specificity.