• We compared a monocomponent pertussis toxoid vaccine preparation (JNIH-7) in a double-blind, randomized study with another component vaccine (JNIH-6) containing pertussis toxoid and filamentous hemagglutinin in equal proportions. Monocomponent pertussis toxoid vaccines have not been tested previously in children. This trial comprised 255 previously nonimmunized children 6 to 10 months old who were given two 0.5-mL subcutaneous injections of either vaccine four to five weeks apart. Prevaccination and postvaccination serum samples from 235 infants showed an antitoxin seroconversion rate of 100% in both groups. Adverse reactions were few and mild, with local reactions occurring more often after administration of the second dose and among recipients of the two-component vaccine (P<.05).