Sera from 87 patients with hepatitis B surface antigen (HBsAg)-positive hepatocellular carcinoma (HCC) and from 29 HBsAg-positive hospital controls were tested for delta (delta) antigen with an immunoenzymatic procedure and for anti-delta antibody, hepatitis Be antigen (HBeAg) and antibody to HBeAg (anti-HBe) by radioimmunoassay. All the sera, from both the HCC cases and the control patients, were negative for delta-antigen. Among the HCC cases 9 were positive for serum anti-delta (10%) whereas among the controls none was positive for this antibody (p = 0.067); the anti-delta-positive cases were found only among HCC patients negative for HBeAg. The lower prevalence of anti-delta among HBsAg-positive HCC patients, as compared to the corresponding prevalence among HBsAg-positive patients with chronic active hepatitis or cirrhosis (reported in the literature) indicates that the pathogenesis of HCC is frequently independent of the pathogenesis of the other HBsAg-positive common chronic liver diseases. By contrast, the higher prevalence of anti-delta among HBsAg-positive HCC cases than among HBsAg-positive controls may reflect the longer average duration of the carrier state in HCC patients (until integration is accomplished and the induction period completed). Serum HBeAg was higher among HBsAg-positive HCC patients with cirrhosis (23%) than among HBsAg-positive HCC patients without cirrhosis (6%) or HBsAg-positive controls (3%); thus, the conflicting results in the literature concerning the association of the HBeAg/anti-HBe system with HCC may be accounted for, in part, by the variable association of HCC with an underlying cirrhosis.