 Participation requires 3 visits over 1-5 weeks. The first visit Screening will help determine subjects eligibility through medical history, physical exam, lung function testing, and exercise testing. Those who qualify will be invited back to 2 test visits, at which subjects will undergo lung function testing and high-resolution CT scans before and after treatment with one of the study drugs. All subjects will take both study drugs: those who are randomized to Perforomist at Test Visit 1 will take Foradil at Test Visit 2, and vice versa. 