We investigated the effect of inhaled glucocorticoid (GC) on bronchial obstruction and on bronchial lability in schoolchildren born preterm. Twenty-one children with bronchial obstruction, increased responsiveness to a beta2-agonist, and/or increased diurnal variation in peak expiratory flow (PEF) were selected for an open longitudinal study of the value of inhaled GC. None of these children had an earlier diagnosis of asthma or current GC treatment. Eighteen children with median (range) birth weight 1025 (640-1600) g and gestational age 28 (24-35) weeks, age at study 10.1 (7.7-13) years, were treated with inhaled budesonide in initially high (0.8 mg m(-2) day(-1) for 1 month) and subsequently lower dose (0.4 mg m(-2) day(-1) for 3 months). Daily symptom scores were recorded. Spirometric values were measured in the clinic at the beginning and end of each treatment period. At home, children used a data storage spirometer. After treatment with budesonide for 4 months, spirometric values in the clinic did not significantly change. The median forced expiratory volume in 1 sec (FEV1) was 74% of predicted both at entry and after budesonide treatment. However, the median number of > or = 20% diurnal change in PEF values at home decreased during treatment. According to the present study, inhaled budesonide for 4 months had no significant effect on basic lung function but may decrease bronchial lability in schoolchildren born preterm.