The present invention describes peptides and recombinant proteins containing Hepatitis C virus core protein sequence in which one or more of the amino acids have been modified or deleted to remove the ability of these proteins to bind to specific anti-HCV murine monoclonal antibodies. The deletions and modifications are designed as to maintain the ability of this protein to be used in immunoassays used for the detection of anti-HCV antibodies in individuals infected with HCV.