The resulting data set was used to test diverse hypotheses concerned with lower respiratory tract illnesses (LRI), asthma, wheezing, allergy, and smoking. There were four broad areas: 1) effects of LRI during the first three years of life and early and late symptoms and allergic sensitization on the picture of asthma; 2) changes during adolescence in symptoms and airways responsiveness; 3) the natural history of allergic sensitization and its relation to asthma and asthma-like symptoms; and 4) the change in longitudinal lung function and factors affecting the change.