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Summary Objective To assess the immunogenicity of a fully liquid diphtheria–tetanus–five component acellular pertussis–inactivated poliomyelitis– Haemophilus influenzae type b (DTaP–IPV–Hib) conjugate vaccine compared to DTaP–IPV and lyophilized Hib conjugate vaccines given simultaneously at separate sites as a three-dose primary vaccination in Taiwanese infants. Methods Two hundred infants were randomized to receive either DTaP–IPV–Hib or DTaP–IPV plus Hib vaccine at 2, 4, and 6 months of age. Both combined vaccines contained the same five pertussis antigens: pertussis toxoid (PT), filamentous hemagglutinin (FHA), pertactin (PRN), fimbriae 2 and 3 (FIM 2&3). Antibody concentrations were measured before the first and after the third dose. Reactogenicity was evaluated from parental reports. All subjects received hepatitis B vaccine at 0, 1, and 6 months of age following the national vaccination schedule of Taiwan. Results The immunogenicity after the third dose was high for each vaccine antigen in both groups, and the vaccines had low reactogenicity. Statistical analysis showed no differences in the immune responses to the fully liquid DTaP–IPV–Hib vaccine compared with those to the DTaP–IPV plus Hib control vaccines, notably the anti-PRP (polyribose ribitol phosphate capsular polysaccharide) response, with 97–99% of infants having concentrations ≥1.0μg/mL. Approximately 95% of all infants developed seroprotective levels of anti-hepatitis B surface antigen (HBs) antibodies (≥10mIU/mL). Conclusions Both combination vaccines had similar high immunogenicity for each antigen, and both were well tolerated. Thus, inclusion of a Haemophilus influenzae type b conjugate vaccine in the combination did not result in clinically significant decrease in the PRP response or increase reactogenicity. The fully liquid pentavalent vaccine has the advantages of not requiring reconstitution and of administration as a single injection.