The aim of this study was to interpret the antibody response to hepatitis B (HB) vaccination following a two booster dose schedule in 94 acute lymphoblastic leukemia (ALL) patients. All patients were between 1-16 years of age with negative hepatitis B virus (HBV) serology and normal hepatic function. Fifty patients were vaccinated with Engerix B vaccine, and 44 patients were vaccinated with GenHevac B vaccine, with a schedule of 0, 1, 6 and 0, 1, 2, as well as booster doses, in 12 and 6 months respectively. A second booster was given as a fifth dose to 16 unresponsive patients in each vaccine group, 3 and 6 months after the first booster for Engerix B and GenHevac B vaccines respectively. Dosage was 20 mug HbsAg for all patients. Seroconversion rates with protective level antibody were 35.1% (n = 33/94). The figures were 32.1% (n = 16/50) and 38.6% (n = 17/44) for Engerix B and GenHevac B vaccines, respectively. Seroconversion rate in patients younger than 10 years old was found to be higher (39.11%) than older patients (24%), but this was not statistically significant. This study indicates that one third of the leukemic children undergoing maintenence chemotherapy responded to HB vaccine with protective titers of anti-HBs. We recommend HB vaccination especially in developing countries. (C) 2001 Elsevier Science Ltd. All rights reserved.