BACKGROUND: Familial aggregation of the phenotypes can be caused by common environmental and genetic factors, but there has been no family study on familial aggregation of the bronchial asthma, and genetic role of atopy and bronchial responsiveness in the development of asthma in Korean families. OBJECTIVE: We did family study to evaluate the familial aggregation of bronchial asthma, and the genetic role of atopy and bronchial responsiveness in the development of asthma. MATERIALS AND METHODS: Questionnaire, serum total IgE level, skin prick test with 10 common aeroallergens, and bronchial responsiveness to methacholine were performed in 154 parents of atopic asthmatics, 72 parents of atopic control, and 65 parents of non-atopic control. RESULTS: Bronchial asthma was more prevalent in parents of atopic asthmatics(7.1% ) than in parents of non-atopic control(0% ). Geometric mean of serum total IgE level was not different among parents of atopic asthmatics, atopic control, and non-atopic control(2.03+0.06, 2.10 +0.07, and 1.89 +0.09 IU/ml). Positive rates of skin prick test to 10 common aeroallergens were more prevalent in parents of atopic asthmatics(43.0% ) and atopic control(43.0% ) than in parents of non-atopic control(27.8%). Prevalence of bronchial hyperresponsiveness to methacholine was more prevalent in parents of atopic asthmatics(17.0% ) than in parents of atopic control(7.2%) and non-atopic control(1.5%), and slope of dose-response curve was more increased in parents of atopic asthmatics(11.0+ 1.5) than in parents of atopic control and non-atopic control(4.8+ 0.7 and 3.0+ 0.5). CONCLUSION: Bronchial asthma runs in Korean families, and genetic role of atopy and bronchial responsiveness may be important in the development of asthma.