We have studied the bronchial hyperresponsiveness of children with atopic and nonatopic asthma by methacholine inhalation challenge, using a new device, the "Astograph." Three parameters, initial respiratory resistance (Rrs cont), bronchial sensitivity (Dmin), and bronchial reactivity (St), were studied. The Rrs cont values of atopic asthma were higher than those of the disease controls (p less than 0.05), while there was no difference between nonatopic asthma and disease controls. The Dmin values of atopic and nonatopic asthma were lower than those of disease controls (p less than 0.001; p less than 0.01). The St values of atopic and nonatopic asthma were higher than those of disease controls (p less than 0.001; p less than 0.01). There was no difference of Rrs cont and Dmin between the children with atopic and nonatopic asthma. However, St of the children with nonatopic asthma was remarkably higher than that of the children with atopic asthma (p less than 0.001). These data suggested that there was a remarkable difference of bronchial response to methacholine between the children with atopic asthma and those with nonatopic asthma.