The prevalence of circulating immune complexes (CIC), their role and their relationship to cell-mediated immunity in patients with hepatitis B virus associated liver disease are still controversial. This study was designed to investigate the prevalence of CIC and their relationship to viral markers, to subsets of peripheral blood T lymphocytes and to suppressor cell activity in patients with hepatitis B virus associated liver diseases. CIC were positive in 29.3% of 41 healthy HBsAg carriers, 37.8% of 88 patients with hepatitis B virus associated liver diseases, and 15% of 41 healthy subjects by the platelet aggregation test (PAT). The prevalence of CIC in patients with acute hepatitis (40.0%) and in those with cirrhosis (61.5%) was significantly higher than in normal controls (p less than 0.05, p less than 0.005 respectively). There was no correlation between the titer of CIC and serum HBsAg titer or the status of HBeAg, and no significant decrease in the peripheral blood lymphocyte CD4/CD8 ratio in healthy HBsAg carriers (1.39 +/- 0.31) and in patients with liver diseases (1.40 +/- 0.54) compared to the normal controls (1.48 +/- 0.31). Concanavalin A induced suppressor cell activity on IgG producing cells was impaired in healthy HBsAg carriers (34.9%) (p less than 0.005) and in patients with liver diseases (25.3%) (p less than 0.0001), and this change was prominent in patients with chronic active hepatitis and cirrhosis (p less than 0.0001). And there was a significant reverse correlation between concanavalin A induced suppressor cell activity on IgG-producing cells and the titer of CIC in PAT positive patients with hepatitis B virus associated liver diseases. In conclusion, it was suggested that defective suppressor cell function may lead to an increased B cell activation and such activity may account for the presence of CIC.