 At the beginning of the study and at the end of the study we will ask that you come in for another visit to do a methacholine challenge breathing test. The challenge involves you breathing a mist that contains a bronchoconstrictor methacholine and then performing spirometry to measure the flow and volume of air in your lungs. You will breathe several different mists, of increasing concentrations of the bronchoconstrictor, until a change in your flow measurement is found. This test measures how sensitive your airways are and takes about 1 hour. You may feel some tightness in your chest andor some wheezing as a result of the challenge, but you will be given bronchodilator medication to reverse the effects of the bronchoconstrictor. You will be closely monitored with spirometry to ensure your safety during this test. 