The objective of this study was to evaluate reactogenicity and immunogenicity of the recently US-licensed Connaught/BIKEN (C/B) acellular DTP (ADTP) vaccine as a booster for children aged 15 to 20 months after they had received either the C/B ADTP or the US-licensed Connaught whole-cell DTP (WDTP) vaccine as infants. After infants had received either three doses of C/B ADTP (n = 109) or three doses of WDTP vaccine (n = 30) at 2, 4, and 6 months of age according to a 3:1, randomized, prospective design, they all received booster doses at 15 to 20 months of age with C/B ADTP. Fever > 101 degrees F (38.3 degrees C), irritability, injection site redness > or = 1 inch, injection site swelling, and injection site pain, among other reactions, were monitored for 14 days after vaccination. IgG antibody to pertussis toxin (PT) and filamentous hemagglutinin were analyzed by enzyme-linked immunosorbent assay and neutralizing antibody to PT was measured by Chinese hamster ovary (CHO) cell assay. No significant differences were observed between the WDTP- and ADTP-primed infants following their ADTP booster for any of the monitored reactions within 72 hours of vaccine administration or in the 4 to 14 days after vaccination. Prior to the ADTP booster, antibody levels were higher in children who had received ADTP compared with those who had received WDTP vaccine as infants for PT antibody as measured by enzyme-linked immunosorbent assay and CHO cell assay. Higher levels of IgG antibody following the ADTP booster were observed to filamentous hemagglutinin and to PT in ADTP-primed compared with WDTP-primed children.(ABSTRACT TRUNCATED AT 250 WORDS)