We describe 5 cases of fulminant hepatitis caused by the HBV infection in patients with haematological diseases, mostly malignancies (ALL, lymphoma, aplastic anemia, AML) following intensive chemotherapy. Infection was confirmed by serological examination (HBsAg positivity) and by electron microscopy (viral particles). After termination of chemotherapy fulminant hepatitis developed with hepatic failure and very high levels of AST and ALT. Autopsy revealed massive necrosis without signs of regeneration. We suggest that immunosuppressive therapy increases the risk of severe infection of hepatocytes with HBV and subsequent withdrawal of chemotherapy causes "immunological rebound" leading to massive necrosis.