High frequency jet devices are not only used as 'internal percussors' to aid clearance of pulmonary secretions, but are also a mode of ventilatory support. As physical stimuli can cause bronchospasm in asthmatic individuals, we hypothesized that direct airway vibration may induce bronchospasm. To ascertain whether an airway vibration jet device could cause bronchoconstriction, we exposed eight asthmatic and six normal subjects to 5 min of jet-induced airway vibration or placebo treatment with cross-over at 3 h. Subjects breathed spontaneously for 5 min through an open mouthpiece into which either jet (10 Hz, 25 psi) or sham pulsations (same device, pressure vented to room at compressor) were delivered in a double-blind, random order. A constant-volume body plethysmography measured functional residual capacity and specific airway conductance (SGAW) and a water seal spirometer measured forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). These pulmonary function measurements were taken before and at 5, 10, 20, 30, 60, 90 and 120 min after each exposure. In the normal subjects there was no significant change in any pulmonary function. There was not statistically significant change in the pulmonary function in the asthmatic patients. However, the oral high frequency oscillator induced a clinical asthmatic attack in one asthmatic patient. In this one patient, the FEV1 fell 35% from its initial value at 5 min following exposure to a maximum of 49% decline from initial value at 1 h following exposure.(ABSTRACT TRUNCATED AT 250 WORDS)