During the period 1986-1988, the expression of anti-HDV in different high-risk groups and its clinical impact on patients with HBV-related chronic liver disease and hepatocellular carcinoma was investigated in Iran. Using the ELISA technique, we observed a 2.5% anti-HDV positivity in asymptomatic chronic HBsAg carriers (3 of 120); in hemophiliacs, two of six HBsAg carriers were positive for anti-HDV and zero of 50 anti-HBs positives. Anti-HBs positive dialysis patients were positive for anti-HDV in 2.0% of the cases (1 of 50), whereas the rate of anti-HDV positivity was 44.5% in hemodialysis patients positive for HBsAg (16 of 36). The figures were comparable in HBsAg positive patients with chronic active hepatitis and cirrhosis (49.2%; 31 of 63). Moreover, anti-HDV was detected in five of eight patients with hepatocellular carcinoma. These data indicate the endemicity of delta infection in Iran. The increased incidence among hepatocellular carcinoma patients is an interesting finding to be further investigated with larger groups of patients in this region.