Asthma is an increasingly common disease caused by bronchial inflammation and characterized by bronchial hyperresponsiveness and intermittent airways obstruction. The development of asthma is most likely determined by an interaction between host susceptibility and environmental exposures. Bronchial hyperresponsiveness (BHR) and elevated total serum IgE levels, characteristic findings in asthma, have been shown to have strong genetic components. The identification of the genetic factors that regulate susceptibility to asthma has important public health consequences, and may lead to an improved understanding of the pathogenesis of asthma. This may lead to improved preventive measures and new therapeutic approaches.