A review of the effects of passive smoking on pulmonary function has been made. In children, there is still a great deal of confusion and controversy. The range of the many effects studied is limited; most prospective studies show small effects. In general, it appears that respiratory infections in children may be increased with passive smoking. The effects on children's pulmonary function ranges from 0 to 3% over the age range from conception to 20 years; these differences in absolute magnitude are considered small. In healthy adults, the effects on pulmonary function and symptoms are not considered to be of concern; the effects in asthmatics require further study. A study to evaluate the above effects is presented here. It derives from a prospective study of airway obstructive diseases in Tucson, Arizona. From that study, it was concluded that the effect of passive smoking on pulmonary function or respiratory symptoms (recorded on a daily basis) in children is not positive. Effects may be seen with regard to responses to other irritants in passive-smoking children. In adults, no effect was seen, even in those with asthma or airway obstructive diseases; this may be due to low dosage. It is concluded that further, more appropriate studies are needed to understand the role of passive smoking on pulmonary function.