The CSGA was composed of five centers (Johns Hopkins University, University of Chicago, University of Maryland, University of Minnesota, and a data coordinating center at Wake Forest). At each center, families were ascertained through two siblings with asthma. All family members were characterized with spirometry, bronchial responsiveness to methacholine or reversibility testing, skin-tests and questionnaire data. The initial genome screen was completed on the first 237 sib pairs from three racial groups (African-American, Caucasian and Hispanic), and genotyping on the remaining family members and families was completed before the study was renewed in 1997. Therefore, the initial aim of the CSGA to map susceptibility regions was completed, with detection of several novel chromosomal regions, and replication of several regions previously linked to associated phenotypes.