This trial assessed the immunogenicity, safety and reactogenicity of a two-dose hepatitis B immunisation regimen (thiomersal-free Engerix-B 20 microg HBsAg doses 6 months apart) compared to the standard three-dose vaccination regimen (preservative-free Engerix-B 10 microg HBsAg doses, 0, 1, 6 month dose schedule) in healthy adolescents aged 11-15 years. Subjects were randomly assigned (2:1 ratio) to one of the two regimens (258 to the two-dose [20 microg] and 126 to the three-dose [10 microg] regimen) (Study ID 103860/280). One month after the final vaccine dose, the seroprotection (anti-HBs >or=10mIU/ml) rate in the two-dose (20 microg) group (233/241 individuals -96.7% seroprotected) was non-inferior to the seroprotection rate in the three-dose (10 microg) group (111/113 individuals -98.2% seroprotected). Both regimens were shown to be safe and well tolerated. Two doses of Engerix-B (20 microg HBsAg) could be considered as an alternative to standard three-dose Engerix-B (10 microg HBsAg) immunisation for adolescents aged 11-15 years.