The presence of the anti-HCV antibody was investigated in sera from 102 chronic HBsAg carriers. The subjects varied as to the characteristics of the clinical states. It was found that HCV coinfection was more common in HBsAg positive intravenous drug addicts than in other parenteral risk groups. It also appears that HCV may be the causative agent of chronic liver disease in HBsAg carriers with undetectable HBV (and possibly HDV) replication.