Bronchial asthma is a chronic disease characterized by episodic small airway obstruction that is clinically manifested by wheezing dyspnea, cough, and production of mucoid sputum. Although asthma can develop at all ages, approximately half of the cases occur before age 10. The incidence in the United States and other countries is about 3% of the population but is very low among American Indians, Eskimos, and West Africans.