A total of 1,566 children the area of Valencia (Spain), of both sexes and aged 7 to 14 received an epidemiological questionnaire recommended by the American Thoracic Society. Antecedents of asthma were recorded in 79 cases (5%), with a predominance among males; 73.3% of these children presented their first crisis before age three. Eighty-seven children were habitual smokers (5.6%), again with a predominance among males-most of these children being between 13 and 14 years old. A family history of smoking was observed in 82.8% of the children who were habitual smokers. A greater predominance of smoking mothers was observed at higher socio-economical levels--with no significant differences between parents. The incidence of respiratory pathology (cough and antecedents of bronchitis) was higher among children whose mothers (or both parents) were smokers. On comparing the two areas of the city with the greatest difference in air pollution level, no significant differences were observed in respiratory morbidity among the child population.