Anti-idiotypic antibodies (anti-Id Ab) against antibodies to HBs, pre-S1 and pre-S2 antigenic domains of the HBV surface protein were searched for by enzyme-linked immunosorbent assay in single serum samples of 57 patients, chronic HBsAg carriers. IgG and/or IgM anti-Id Ab were detected in 15 patients (26%). IgG and / or IgM anti-[anti-HBs] anti-Id Ab were found in 8 serum samples (14%) and they appeared to occur more frequently in patients seropositive for HBeAg than in these seropositive for anti-HBe. IgG and / or IgM anti-[pre-S1] anti-Id Ab and IgG and / or IgM anti-[anti-pre-S2] anti-Id Ab were detected in 5 (9%) and 8 (14%) patients, respectively. Both these anti-Id Ab were found more frequently in patients seropositive for anti-HBe than in patients seropositive for HBeAg. Anti-[anti-pre-S2] anti-Id Ab occurred more frequently in patients with sever liver damage than in these with near normal liver or established cirrhosis.