In 1975 a stratified, random sample of propositus children ages 5-9 living in the East Boston area of Boston, Massachusetts was selected as were their family members to form the cohort. In the longitudinal study, each member of the propositus cohort and all family members five years of age and older residing in the household were visited at home annually by study personnel. Data collected included: a respiratory illness history; demographic data on type of heating, fuel for cooking, types of air-purifying devices, and area of residence; cigarette smoking history; disability from cardiac disease; age of puberty in female children; pulmonary function tests; and anthropometric data. The study helped to determine the extent to which airways responsiveness was a risk factor for chronic airflow obstruction, was acquired as a result of other exposures or as a consequence of chronic symptoms or lower levels of pulmonary function.