The results of the following studies are reported: a longitudinal double blind trial comparing Lederle-Takeda APDT vaccine with Lederle DTP vaccine in two, four and six month old infants; two double blind similar APDT vs DTP trials in 18 month old and four to six year old children; a large longitudinal open trial with APDT in two, four and six month old infants and a household contact efficacy trial with Takeda APDT in Japan. APDT vaccine recipients had a lesser frequency and less severe reactions than whole cell vaccine recipients. Antibody responses to lymphocytosis-promoting factor and agglutinogens were higher in DTP recipients; APDT recipients had a better serologic response to filamentous hemagglutinin. Equivalent 69K protein antibody responses were seen. Vaccine efficacy in the household contact study was 98% (95% CI = 84% to 99%) against classical pertussis and 81% (95 CI = 64% to 90%) if all respiratory illnesses are considered.