This study assessed the immunogenicity and safety of two vaccination regimens that employed either GSK Biologicals' combined DTPa-HBV-IPV/Hib vaccine or DTPa-IPV/Hib vaccine. In the two groups, infants received the DTPa-IPV/Hib vaccine at 3 and 4 months of age, as the first 2 doses of the primary vaccination course. At 5 months of age, they received either the DTPa-IPV/Hib vaccine co-administered with the HBV vaccine or a dose of the DTPa-HBV-IPV/Hib vaccine as a 3rd dose. Infants in the two groups had previously received 2 doses of HBV vaccine at birth and at 1 month of age.