Using histamine inhalation tests, we followed changes in bronchial hypersensitivity in 48 children with atopic dermatitis (AD) who were nonasthmatic on their initial visit. Twenty-three of these subjects became asthmatic during the follow-up period. The respiratory thresholds to histamine RT-Hist) of children with AD were widely distributed, ranging from 156 to more than 5000 micrograms/ml. There was a statistical difference in RT-Hist, as those who became asthmatic showed lower levels (< or = 625 micrograms/ml) at 2-6 yr of age. The percentage of peripheral eosinophil counts and IgE level was significantly elevated in those who became asthmatic. Subjects who developed asthma were more likely to have had positive D.p. RAST when they were less than 2 yr of age. The development of asthma in children with AD showed no significant relationship with family history of bronchial asthma.