The authors analyzed an epidemic of viral hepatitis B during which 43% patients of the haemodialy- zation centre in K were infected. Using the method of sequence analysis of the DNA of hepatitis B virus they identified the source of infection. They monitored serologically the course of infection in all infected subjects and the state of specific antibody immunity in patients and staff. 22% infections were manifested clinically and 75% infected HBsAg positive patients developed chronic hepatitis. Although 38 of 42 haemodialyzed patients were vaccinated against hepatitis B, 20 patients lacked anti-HBs antibodies before the epidemic. Only one of the patients without anti-HBs was not infected. In 10 immune patients the rise of antibody levels confirmed that they were also exposed to HBV. The effectiveness of vaccination against VHB in haemodialyzed patients is markedly lower. Vacci- nation of these patients is an important but only supplementary provision in VHB prevention. Sequence analysis of HBV DNA may be a useful tool of epidemiological analysis.

        Key words: hepatitis B – haemodialysis – sequential DNA analysis – immunization.