Induced sputum: An ultrasonic nebuliser is filled with 3% saline and subjects inhale the nebulised solution for 7 minutes following pre-treatment with inhaled salbutamol. After this, the nebuliser is filled with 4% saline and the nebulised solution is inhaled for 7 minutes. Finally, the nebuliser is filled with 5% saline and the nebulised solution is inhaled for 7 minutes. At 5-minute intervals the inhalation is stopped to allow expectoration into a polypropylene container. The sample is kept on ice until processed for cell counts and ultra centrifugation to harvest the soluble phase of sputum. Cell counts will be performed and the supernatant stored for analysis of inflammatory mediators. The test will not be performed on subjects with an FEV1 < 1 L.