Three hundred and twenty eligible infants were enrolled in an open randomized clinical trial and allocated to one of two groups to receive either separate concomitant injections of a candidate combined DTPa-HBV-IPV and commercial Hib vaccine (candidate administration: DTPa-HBV-IPV+Hib) or separate concomitant injections of licensed DTPw-IPV mixed in the same syringe with Hib and HBV vaccines (comparator administration: DTPw-IPV/Hib+HBV). Vaccines were administered at 6, 10 and 14 weeks of age preceded by a monovalent dose of HBV at birth. The candidate vaccine administration was shown to be at least as immunogenic (primary objective) as the candidate administration with respect to the diphtheria, tetanus, polio, HBs and PRP seroprotection rates (primary endpoints). Post vaccination, both vaccine administrations showed an equivalent level of seroprotection with nearly all subjects (>96%) acquiring seroprotective titers against diphtheria, tetanus, polioviruses, HBsAg and PRP antigens. A markedly higher anti-HBs response post dose 2 at week 14 in the group receiving the candidate vaccine, 98.6% of subjects had seroprotective titers (GMT of 505.7 mIU/ml) compared with only 88.7% (GMT of 107.5 mIU/ml) in the comparator group. There was a lower incidence of adverse events following the DTPa-based candidate administration compared with the DTPw-based comparator. Despite the early age and short interval between doses, both administrations were immunogenic, with the concomitant administration of DTPa-HBV-IPV and Hib vaccines showing an improved tolerability over the commercial vaccines DTPw-IPV/Hib and HBV.