Purpose: To utilize standardized procedures to measure the immune response in clinical trials of acellular pertussis vaccine (ACPV). 1. NIAID - Multicenter Phase II Trial: The Laboratory of Pertussis served as the serologic reference laboratory for the multicenter trial of thirteen candidate acellular pertussis vaccines. Four ELISA assays (IgG-PT, IgG- FHA, IgG-69k, IgG fimbriae) and whole-cell agglutinins were performed on over 4000 sera for this study (more than 20,000 individual assay results were reported). As part of the study, FDA methodology and reagents were transferred to the NIAID-supported laboratory which performed confirmatory testing on a 10 percent sub-sample of sera from the study and to the laboratory which performed the CHO-cell testing. (a) FDA scientists advised NIAID statisticians on the procedures for analysing and presenting the serologic data from the NIAID multicenter trial. (b) Quality assurance analyses of the FDA serologic data demonstrated a high reproducibility and consistency of the data generated in the FDA laboratory and demonstrated a high degree of correlation among the results obtained in the three testing laboratories. (c) FDA scientist assisted in presentation of serologic data from the trial to the NIAID Task Force. 2. Development of new assays. Procedures are being developed to measure epitope-specific responses in individuals immunized with acellular vaccines.