Airway responsiveness: Bronchial challenge testing with methacholine will be undertaken using Cockcroft's technique with concentrations of methacholine from 0.03 to 16 mg. A value of methacholine hyperreactivity > 16 mg/ml will be read as 16 mg/ml. Bronchial hyper-reactivity is defined as a PC20 FEV1 of < 8 mg/ml. Methacholine challenge testing will only be performed in subjects who have a baseline FEV1 of greater than 60% predicted.