The relation between exposure to environmental tobacco smoke and childhood asthma is not clear. A 1993 study of 892 subjects age 6-17 years (87.5% of 1,019 eligible subjects) living in Humboldt, Saskatchewan, showed that a lifetime history of asthma and asthma attack during the past 12 months were more common among allergic children than among non-allergic children. The number of household smokers and total daily cigarette consumption by household members were linearly related to both lifetime history of asthma and recent asthma in nonallergic children, but not in allergic children. Out study indicates that allergic status does alter the relation between exposure to environmental tobacco smoke and childhood asthma.