The Laboratory of Pertussis is responsible for routine control testing of pertussis vaccine potency and toxicity. The toxicity and potency of the pertussis vaccine component of licensed vaccines are tested before the product can be released. Control testing in the Laboratory of Pertussis is used to determine that the pertussis component of vaccine issued by U.S. licensed establishments have adequate and stable potency through the dating period and are free from untoward reactivity due to toxicity. Satisfactory estimates of potency, stability and protective units per total human immunizing dose are determined using mice as animal models. In addition, mice are used to determine vaccine toxicity by observing early and late weight changes. On December 17, 1991, the first acellular pertussis vaccine was licensed in the U.S. The consistency of manuyfacturing for lots of acellular pertussis vaccines is tested by a potency test evaluating immunigencity in mice by ELISA and a toxicity test assessing residual PT bioactivity by histamine sensitization in mice. In addition to laboratory examination of each vaccine submitted for release, control testing involves reviewing the manufacturer's protocol for satisfactory production methods and control tests performed by the manufacturer. During the period described by this report, no significant changes in potency and toxicity of pertussis vaccines submitted for release were noted. When materials allow, the Laboratory of Pertussis also performs control testing on vaccines from foreign manufacturers and serves as a reference testing laboratory for the World Health Organization.