In a survey of 1,355 children six- to 12 years of age, the risk of hospitalization for respiratory illness among children before age two years was increased when gas was used for cooking at home (p less than 0.001) or at least one of the parents smoked (p less than 0.02). The occurrence of cough with colds in children also was significantly increased when one or both parents smoked (p less than 0.001). Small but significant increases (p less than .05) in the mean values of forced expiratory volume at one second, the flow rate at 75 percent of the forced vital capacity, and the forced expiratory flow rate from 25 percent to 75 percent of the vital capacity (FEF25-75) were seen after administering inhaled isoproterenol to children whose parents smoked (n = 94) but not among children whose parents did not smoke (n = 89); this was not seen in association with gas cooking. Thus, exposure of children during the first two years of life to gas cooking or cigarette smoking appears to be associated with an increased risk of hospitalization for respiratory illness, and cigarette smoking appears to be associated with a more consistent response to inhaled bronchodilator among six- to 12-year-old children with no other history of chronic respiratory illness.