Antibody to hepatitis-B core antigen (anti-HBc) was assayed in the serum of patients with primary hepatic carcinoma (P.H.C.) and controls from Hong Kong, West Africa, and the United States. In each region the prevalence of anti-HBc was higher in P.H.C. patients than in controls, ranging from 70 to 95% in the patients and from 20 to 68% in the controls from Asia and Africa; 24% of P.H.C. patients and 4% of controls from the U.S. had anti-HBc. These data support the hypothesis that chronic infection with hepatitis-B virus is aetiologically related to P.H.C., especially in Asia and Africa, although other factors must also be involved.