We evaluated bronchial lability and responsiveness in 29 prematurely born children (birth weight < 1,250 g) 8 to 14 yr of age, 12 with histories of bronchopulmonary dysplasia (BPD). Flow-volume spirometry, a bronchodilator test, and histamine challenge at the office and home monitoring of peak expiratory flow (PEF) values twice daily for 4 wk with and without a beta2-agonist were performed with a novel device, the Vitalograph Data Storage Spirometer. The spirometric values at the office and the results of home monitoring were compared with those for a control group of children born at term. All spirometric values except FEV1/FVC were significantly lower in the BPD group than in the non-BPD group (p < 0.0001). Ten children (83%) in the BPD group and four (24%) in the non-BPD group had subnormal spirometric values at the office, indicating bronchial obstruction. Of the children with obstruction, 79% reported respiratory symptoms during the preceding year, and 57% had increased diurnal PEF variation and/or responded to administration of a beta2-agonist during home monitoring or at the office. The BPD children were significantly more responsive to histamine than the non-BPD children (p = 0.002). All spirometric values were significantly lower in both preterm groups than in the control group born at full term (p < 0.01). In conclusion, regardless of BPD, bronchial obstruction, bronchial lability, and increased bronchial responsiveness are common in prematurely born children of school age.