To assess the relevance of HBe/anti-HBe system and DNA polymerase activity in patients on regular dialysis treatment, we prospectively studied 38 patients on haemodialysis, who were chronic carriers of HBs Ag (range 6–66 months), and 26 HBs Ag negative dialysis patients as controls. HBe Ag was present in 74%, DNA polymerase in 60%, and anti-HBe in 13% of HBs Ag positive patients. After a mean follow-up of 23.5 months, only 2 patients, who had been HBe Ag positive, had cleared HBs Ag, and 1 of them had turned to anti-HBS positivity. Among the patients who were still HBs Ag positive, only 1 had lost HBe Ag, without developing anti-HBe. Throughout the study, SGOT and SGPT levels were significantly raised in HB virus carriers as compared to controls. In the HBs Ag positive group, the presence of HBe Ag and/or DNA polymerase characterized a subgroup with the most striking abnormalities in enzyme levels. The causes of death in the HBs Ag positive group were not related to liver disease. Viral replication usually takes place in HB virus carriers on haemodialysis and is associated with biochemical evidence of liver-cell damage. However, the HB virus carrier state, and the underlying liver disease, are not major problems at present in patients on chronic haemodialysi