We evaluated anti-HBs titers 2 months after vaccination with recombinant hepatitis surface antigen (rDNA-HBsAg) in 43 maintenance hemodialysis patients (MHP). Of these, 34 had not undergone hepatitis B virus vaccination previously (NV-MHP) and 9 had shown negative response to vaccination with plasma-derived HBsAg (HEVAC Pasteur; V-MHP). 120 healthy workers from the same hospital undergoing rDNA-HBsAg immunization were used as controls. All low responders (LR) (anti-HBs < 100 mlU/ml) and nonresponders (NR; anti-HBs < 10 mlU/ml) were given a booster dose 3 months after the last dose of vaccine. Seroconversion rates were lower in NV-MHP (52.9%) than in controls (98.4%). V-MHP showed higher seroconversion rates (88.9%) than NV-MHP. In each group, the number of responders (R; anti-HBs ≥ 100 mlU/ml), LRand NR was as follows: controls 101,17,2; NV-MHP 6,12,16; V-MHP 8,0,1. After booster dose, 17/17 controls LR and no NV-MHP LR showed a rise in anti-HBs titers over 100 mlU/ml. Six months after the last dose of vaccine or the booster dose, anti-HBs titer fell under 10 mlU/ml in 4/12 MHP LR and under 100 mlU/ml in 6/14 MHP R. To achieve high seroconversion rates and to avoid the decline of anti-HBs to nonprotective titers in MHP, a booster injection should be made at different dates after the first vaccinatio