Present hepatitis B vaccines use multidose prolonged regimens, which even healthcare workers at risk do not always complete. Moreover, when vaccination is completed there remain some who fail to achieve adequate protection. The protection of adults at risk could be improved if there were a more potent vaccine and/or a shorter vaccination regimen available. Vaccine-naive adults were randomized to vaccination with either Engerix-B (SmithKline Biologicals, Rixensart, Belgium) or a novel triple antigen (S, pre-S1, and pre-S2) recombinant vaccine (Hepacare; Medeva Pharma Plc, Speke, UK). The primary efficacy parameter was the degree of seroprotection 6 or 7 months (26 +/- 2 weeks) after beginning vaccination. A total of 304 adults entered the study. Of these, 16 failed to complete the study (9 on Hepacare and 7 on Engerix-B). With the Engerix-B standard (0, 1, 6) regimen, 88% of subjects were protected by month 7, whereas with the triple antigen vaccine a 2-dose regimen (0, 1) provided equivalent protection (91%) within 6 months and a 3-dose (0, 1, 6) regimen was significantly superior (98% seroprotected by 7 months after starting vaccination P <.001). With adults at risk for a suboptimal response (i.e., older adults, the obese, men, and smokers) the triple antigen vaccine produced a greater degree of protection. The vaccines had similar safety profiles. Both vaccines were well tolerated. In healthy normal adults, a triple antigen hepatitis B vaccine containing S and pre-S antigens produced an enhanced immunologic response and was as effective as a 2- and 3-dose regimen.