The contagiousness of hepatitis B virus (HBV) carriers with end-stage renal disease undergoing chronic hemodialysis has been ascribed to an immunologic tolerance for HBV antigens, especially hepatitis B core antigen, supporting persistently high levels of virus replication. In this context hepatitis B e antigen and core-associated DNA polymerase (DNA P) activity have proved to be distinct markers of HBV replication. In order to evaluate the potential infectivity of these subjects, thirty-five HBsAg positive hemodialysis patients were studied for the presence of HBeAg/anti-HBe system correlating the results with serum DNA P activity. Twenty out of 35 patients were HBeAg positive (57%) and 21 DNA P positive (60%). A highly significant correlation (P less than 0,001) was recorded between detection of HBeAg and presence of serum DNA P activity. These findings confirm that the majority of hemodialysis patients carrying HBsAg show high levels of virus replication so that the determination of HBeAg and DNA P activity other than HBsAg is required for the identification of patients highly infectious.