Serious aggravation of de novo hepatitis B caused by revitalization of the hepatitis B virus in HBs antigen negative, HBs antibody or HBc antibody positive patients has recently been reported. The incidence of de novo hepatitis B infection which occurs in patients undergoing immunosuppression or chemotherapy develops at times into a medical lawsuit. To cope with the situation, the Ministry of Health, Labour and Welfare (MHLW) issued the guideline for the management of hepatitis B infective occurring in patients treated with immunosuppressive therapy or chemotherapy (the revised edition). In our institution, the Chemotherapy Committee discussed our measures against de novo hepatitis B, and determined to carry out the in-hospital examination of the HBc antibody to provide reliable safe and speed medicine.　　During the investigation period, HBc antibody was examined for confirmation of anamnesis of Hepatitis B in patients receiving chemotherapy, immunosuppressive medicine, examination of infectious disease before blood transfusion and examination of viral hepatitis. In our institution, the number of cases which are adapted for the MHLW guideline (the revised edition) was 15 of 218 examples, and as a result HBs antigen negative, HBs antibody or HBc antibody positive patients, who could not be found in the routine screening for HB infection turned out to be not a few.　　Since it was expected that the number of patients undergoing immunosuppression and chemotherapy would continue to increase in the future, the necessity for observance of guideline was suggested to provide relief, safety in medical treatment.