Studies have provided evidence relating acute lower respiratory tract illnesses in the first few years of life to the development of chronic lung disease in later life. Epidemiologic studies have demonstrated that geographic areas with high morbidity and mortality rates due to chronic obstructive lung disease among adults are also likely to show a high incidence of respiratory illness among children. A number of risk factors may be associated with lower respiratory tract illness in children. Some studies suggested that familial or genetic factors may predispose certain children to respiratory disorders early in life. Family size, viral and bacterial infections, allergic reaction, air pollution, gas stoves, formaldehyde, and passive smoking have all been implicated. Research was needed on the interrelationships of potential risk factors and lower respiratory tract infections in producing chronic respiratory disease.