Infection with the virus of hepatitis B is found in haemodialyzed patients many times more frequently than in the normal population and it participates in their morbidity and mortality. It is also an important issue in patients after transplantation of the kidney. With regard to the alarmingly high prevalence of this infection in their haemodialyzation centre the authors analyzed retrospectively the effectiveness of the most successful preventive measure--active immunization--in 84 patients immunized with Engerix B according to the protocol recommended for haemodialyses. They found that: i) active immunization started after the onset of haemodialyzation has a low effectiveness and in patients who do lack protective antibodies anti-HBs before the onset of haemodialysis it is important to look for other preventive measures; ii) a certain effectiveness is achieved only by administration of more than three doses of vaccine.