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In this double-blind, randomized, controlled study, healthcare professionals with a history of inadequate response to currently available single-antigen hepatitis B vaccines confirmed by measuring hepatitis B surface antibody titer before entry to the study were revaccinated with a 20-g dose either of a novel triple-antigen (S, pre-S1, and pre-S2) recombinant vaccine or of a present single-antigen (S only) vaccine. Hepatitis B surface antibody titers were measured 8 weeks' post revaccination. A total of 925 individuals were randomized and vaccinated, of whom 915 (98.9%) completed the study and were included in the efficacy analysis. A single dose of the new triple-antigen hepatitis B vaccine (Hepacare) produced a successful response in over three quarters of these subjects who had not mounted an adequate response to current vaccines. The antibody response was statistically significantly superior (P ‫؍‬ .002) to that after a single dose of current vaccines. An evaluation of the overall response showed that only the triple-antigen vaccine was able to raise the average antibody response (geometric mean titer [GMT]) to over 100 IU/L. The superior effect of the new vaccine was most pronounced in subjects who were previously complete nonresponders to currently available hepatitis B vaccines. Both vaccines were well tolerated and had similar safety profiles. This study demonstrated that in healthcare workers who had responded inadequately to at least a full course of immunization (median, 5 doses), a single 20-g dose of a new triple-antigen vaccine induced protective antibody level in more vaccinees (P ‫؍‬ .002) and increased the average antibody titer (GMT) in those protected successfully to a greater degree (P < . 001) than a further attempt with a current vaccine (Engerix-B). (HEPATOLOGY 2001;34:798-802.)It is estimated that more than 2 billion people worldwide have been infected by the hepatitis B virus (HBV), and that currently there are about 350 million carriers. 1 Vaccination is the only approach to eradication of the disease, and the adoption of universal childhood vaccination against hepatitis B is now recommended 2 and implemented in some 100 countries. However, these programs have only been adopted in the last decade or so, and therefore there is a continuing need to protect those at high risk such as physicians and ancillary healthcare workers. 3 In this context, it is important to recognize that present vaccination programs are not completely successful, and that 10% to 15% of the normal adult population fail to produce hepatitis B surface antibody (anti-HBs) titers above the critical values for protection (10 IU/L). 4,5 The HBV consists of an inner core and an outer surface coat (hepatitis B surface antigen [HBsAg]). The inner core contains double-stranded DNA, DNA polymerase, hepatitis B core antigen, and the e antigen. Several antigenic determinants (a, d, y, w, and r) are found on HBsAg particles. The HBV genome consists of several open reading frames in addition to that for the common surface antigen...