A new five-component acellular pertussis (AP) vaccine containing 10 µLg of pertussis toxoid,S µg of filamentous hemagglutinin, 5 jµ of combined agglutinogens 2 and 3, and 3 µg of pertactin was evaluated in adults and young children. AP vaccine was compared with saline placebo in 31 adults, and AP vaccine combined with diphtheria and tetanus toxoids (ADTP) was compared with whole cell DTP in 41 children, ages 16–20 months, who had received whole cell DTP during infancy. AP was mildly to moderately reactogenic in adults, with pain noted within 72 hand 5–8 days after immunization. ADTP was less reactogenic than DTP in children, with significantly decreased pain, redness, irritability, and fever and less use of acetaminophen reported. No late reactions were observed in any child. The multicomponent ADTP was immunogenic, with fourfold or greater antibody rises to at least four pertussis antibody assays in allIS immunized adults. Pertussis-specific antibody responses in children who received ADTP and DTP were similar. The multicomponent ADTP vaccine is currently being studied in a National Institute of Allergy and Infectious Diseases-sponsored efficacy study in Sweden.