A study was undertaken to assess the state of hepatitis B virus (HBV) infection in hemodialysis patients. From 97 hemodialysis patients tested, 51 were found to have at least one hepatitis B virus specific marker. 18 were HB<sub>S</sub>Ag carriers, 12 of these carriers have to be regarded as infectious as judged from the presence of HB<sub>e</sub>Ag and/or HBV-specific DNA polymerase activity in the serum. Antinuclear antibodies (ANA) were found in the sera of approximately 20% of the hemodialysis patients with a high prevalence in cases which lacked HBV markers. We conclude from our study that HB<sub>S</sub>Ag-positive hemodialysis patients should be dialyzed in a separate unit and preferably served by personnel which is anti-HB<sub>S</sub>-positive. The question whether patients in which anti-HBc represents the only HBV marker should be separated is still open and needs further work. The role of non-A/non-B infection is difficult to determine and further studies are needed to elucidate this question.