The aim of this study was to interpret the antibody response to hepatitis B vaccination following an intensified four-dose schedule in 140 cancer patients who presented at our clinic between January 1, 1993 and December 31, 1994. According to therapy status, the patients were divided into two groups: group A consisted of 76 patients undergoing chemotherapy and group B of 64 patients in complete remission and off treatment. The eligibility requirements were negative hepatitis B virus (HBV), HCV, and human immunodeficiency virus serologic markers. A total of four dose (20 micrograms per dose) of recombinant HB vaccine was administered intramuscularly in the deltoid region at 0, 1, 2, and 6 months. Blood from the vaccinated subjects was obtained at months 1, 2, 3, and 7 in order to measure anti-HBs titer levels. Protective anti-HBs titers were considered to be those > or = 10 mIU/mL. The overall seroconversion rate 1 month after the fourth dose was 57% (80/140 patients), and the seroconversion rates for groups A and B were 31.5% (24/76 patients) and 87.5% (56/64 patients), respectively. Our results indicated that immunocompromised children undergoing chemotherapy (although less responsive than children in complete remission and off treatment) still preserved their potential to produce protective titers of anti-HBs. On this basis we recommend (1) HB vaccination after diagnosis of malignancy in pediatric patients whenever a high prevalence of HB infection exists and (2) vaccination of patients of therapy and in complete remission.