Objectives: (a) To evaluate the serologic response to infection with B. pertussis and immunization with pertussis vaccine (b) To determine which serologic assays have the highest diagnostic sensitivity and specificity for pertussis and (c) To understand pertussis epidemiology in the community through seroprevalence and outbreak studies. (1) CDC Multicenter Surveillance Study: Evaluation of data collected for this study has continued. A manuscript has been published in which these data were used in the analysis of the efficacy of whole cell pertussis vaccines in U.S. children four years of age and younger. (2) Serodiagnosis: (a) Assays are in place to measure IgG, IgA, and IgMantibodies to PT, FHA, LOS, pertactin, fimbriae, and whole bacteria. These 18 assays plus the whole-cell microagglutination assay have been performed on paired sera from immunized and infected individuals. No single assay has the required characteristics and analyses are underway to select the optimal combination of assays. (b) Historical data have shown that for children immunized with whole-cell vaccine, pertussis agglutinating antibodies correlated with clinical protection. Analysis of the serologic data indicates that IgG anti-fimbriae antibodies correlate best with agglutinins in immunized children while IgG and IgA anti-fimbrial antibodies correlate well with agglutinins in convalescent individuals. (3) IgG and IgA antibodies to Pt, FHA, pertaction and fimbriae have been measured in serial serum samples collected from 72 Japanese individuals with culture-confirmed pertussis.