Sera of 803 hemodialysis patients and 413 staff members were tested to evaluate the relationship between infectivity markers and spread of HBV infection in dialysis units. HBsAg was detected in 13.8% patients undergoing chronic hemodialysis and 3.9% staff members. High prevalence of HBeAg and DNA polymerase activity was observed only in HBsAg positive patients. The highest titers of HBsAg and anti-HBc were detected in hemodialysis patients, whereas asymptomatic carriers showed low titers of these markers. A highly significant correlation was recorded between detection of HBeAg in patients and presence of serum DNA activity. These data suggest that in HBsAg hemodialysis patients a more active viral replication occurs and a higher contagiousness of these subjects.