One hundred thirty-five hepatocellular carcinomas were examined for the presence of antigenic tumor markers by the avidin-biotin-peroxidase complex method. Ninety-seven were from the US and 38 came from Argentina. The following markers were tested: alpha-fetoprotein (AFP), alpha-1-antitrypsin (AAT), hepatitis B surface antigen (HBsAg), hepatitis B core antigen (HBcAg), hepatitis D delta antigen (HD delta Ag), and Mallory's bodies (MB). In the US cases, AFP was present in 43%, AAT in 41%, HBsAg in 17%, and MB in 48%. Both HBcAg and HD delta Ag were absent. In the cases from Argentina, AFP was found in 26% and AAT in 18%. None of the other antigens were seen. Thirteen US tumors expressed three antigens and two four antigens simultaneously. This study reveals in humans a heterogenous expression of antigens by neoplastic hepatocytes with geographic differences, possibly due to multiple factors such as alcohol consumption or prevalence of hepatitis B infection.