Abstract: The aim of this study was to determine the carrier rate of hepatitis virus in patients with haematological malignancies and the incidence of liver injury in these patients following chemotherapy. From January 1996 to September 2002, we studied 601 consecutive, unselected series of patients with haematological malignancies admitted in our hospital unit (Japan). They consisted of 246 cases of acute leukaemia, 218 non-Hodgkin's lymphoma (NHL), 13 adult T-cell leukaemia, and 124 multiple myeloma. Of these 601 patients, 373 were men and 228 were women; their mean age was 61 yr, with a range from 18 to 89 yr. The prevalences of hepatitis B virus (HBV) and hepatitis C virus (HCV) were 7.3% and 10.1%, respectively, in NHL, both higher than those in acute leukaemia (1.7% and 2.9%, P < 0.005) and in general Japanese population (1.2% and 2.6%). The incidence of post-chemotherapy liver injury in 25 HBV carriers (36.0%) was significantly higher than that in 539 non-hepatitis virus carriers (12.6%, P = 0.003) and 37 HCV carriers (10.8%, P = 0.026). Liver injury in HBV carriers was more often present in patients who had been treated with steroids than in those without steroids (72.7% and 0%, P = 0.013). After lamivudine became available in our institution, the incidence of liver injury in HBV carriers was reduced from 53.3% to 10.0% (P = 0.041). The therapeutic strategy for haematological malignancies in hepatitis virus carriers should be further investigated.