Peripheral airways resistance (Rp) has been shown to be increased in asymptomatic asthmatic patients with normal spirometric values, and to be correlated with airways hyperresponsiveness to methacholine. We investigated whether Rp in asthmatic subjects with exercise-induced bronchospasm (EIB) would rise in response to cool, dry air. Using a wedged bronchoscope technique, we challenged an isolated lung segment with high flows (500 to 1,000 ml/min) of cool (22 degrees C) dry 5% CO2 in air for 5 min in eight asthmatic subjects with EIB and eight normal subjects. Baseline Rp and Rp following challenge were measured with saturated air at 37 degrees C at a flow rate of 100 ml/min. Baseline Rp was significantly greater in the asthmatic (0.09; [0.05 to 0.23] cm H2O/ml/min; median [interquartile range]) than in the normal subjects (0.05; [0.03 to 0.07] cm H2O/ml/min) (p = 0.04). The asthmatic, but not the normal subjects, had a significant absolute maximal increase in Rp following cool, dry air (0.10 [0.03 to 0.15] cm H2O/ml/min) (p < 0.01). In the asthmatic subjects, baseline Rp correlated with airways hyperresponsiveness to exercise (r = -0.76, p = 0.03). We conclude that the peripheral airways of asthmatic individuals with EIB are responsive to cool, dry air, and may play an important role in EIB.