The hepatitis C core antigen (HCVcAg) derives from the hepatitis C virus (HCV) core protein. This protein, located on the first 192 amino acids of the N-terminal of the polyprotein, assembles into the nucleocapsid enclosing the genomic RNA. Core proteins p21 and p19 are included within this region. Structure and functions of these core proteins are relatively poorly understood. Antibodies that recognize the HCV core antigen are useful in assays to detect the presence and abundance of HCV.