STUDY OBJECTIVES: The aim of the present study was to evaluate the forced oscillation technique (FOT) in cystic fibrosis (CF) children and to participate in the discussion about the usefulness of beta2-antagonists in CF. DESIGN: Pulmonary function was measured with spirometry, body plethysmography, and FOT before and after inhalation of 200 microg of albuterol (salbutamol). The following were collected: vital capacity (VC), FEV1, FEV1/VC, airway resistance (Raw), thoracic gas volume, respiratory system resistance (Rrs) and respiratory system reactance (Xrs) at 6 Hz (Rrs6 and Xrs6), and resonance frequency. SETTING: The study was set up at a university hospital with a CF population of 125 children and adolescents. PATIENTS: Data were collected on 20 patients in stable condition able to perform the three lung function tests. MEASUREMENTS AND RESULTS: Mean baseline values (+/-SD) were 0.36+/-0.15 kPa/L/s for Raw, 0.5+/-0.15 kPa/L/s for Rrs6, and 61+/-22% predicted for FEV1. The relationship between FEV1 and Raw or Rrs6 was poor. Xrs6 and FEV1/VC correlated weakly (r=0.56; p < 0.05). After bronchodilator administration, the mean changes +/-SD in percent of baseline were +3 +/- 11% for FEV1, -16 +/- 22% for Raw, and -16 +/- 9% for Rrs6. In six patients, a paradoxical decrease in FEV1 was measured but an increase in Rrs6 was never found; in two patients, an increase of Raw of < 10% was found. In 13 patients, the decrease of Rrs6 was > 12%. CONCLUSIONS: The results suggest that FOT measurements cannot replace baseline spirometric measurements in CF, but that the evaluation of the effect of beta2-agonists on the airway diameter in CF should include an FOT measurement.