Background: Chronic rejection, manifesting as bronchiolitis obliterans, is the leading cause of death in lung transplant recipients. In our previously reported double-blinded, placebo-controlled trial comparing inhaled cyclosporine (ACsA) to aerosol placebo, the rate of bronchiolitis-free survival improved. However, an independent analysis of pulmonary function, a secondary endpoint of the trial, was not performed. We sought to determine the effect of ACsA, in addition to systemic immunosuppression, on pulmonary function. Methods: From 1998-2001, 58 patients were randomly assigned to inhale either 300 mg of ACsA (28 patients) or placebo aerosol (30 patients) 3 days a week for the first 2 years after transplantation. Longitudinal changes in pulmonary function of ACsA patients were compared to aerosol placebo patients. In another analysis, the rate of decline from 6-month maximum FEV 1 in randomized patients was compared to the rate of decline in patients receiving conventional immunosuppression from the Novartis transplant database (644 patients, 12 centers worldwide, transplanted from 1990-1995). Results: The average duration of ACsA and aerosol placebo was 400 days AE 306 and 433 AE 256, respectively. The change in FEV 1 of ACsA patients (adjusted for Cytomegalovirus (CMV) mismatch and transplant type, followed for a maximum duration of 4.6 years) was superior to the aerosol placebo controls (9.0 AE 71.4 mL=year vs. À107.9 AE 55.3, p ¼ 0.007). The FEF 25-75 decreased by À220.3 AE 117.7 L=(secondÂyear) vs. À412.2 AE 139.2, p ¼ 0.07, respectively. Similarly, percent FEV 1 decline from maximal values was improved in ACsA patients compared to aerosol placebo and Novartis controls (ACsA À0.43 AE 1.12%=year vs. aerosol placebo À4.08 AE 1.4, p ¼ 0.04; ACsA vs. Novartis À4.7 AE 0.31, p ¼ 0.007). Single-lung recipients receiving ACsA showed improvement in FEV 1 compared to Novartis controls (FEV 1 À0.8 AE 1.8%=year vs. À4.94 AE 0.4, p ¼ 0.03) but double-lung recipients showed improvement compared to aerosol placebo controls only (FEV 1 À0.28 AE 1.22%=year vs. À8.53 AE 5.95, p ¼ 0.048). Conclusions: In this single center trial, ACsA appears to ameliorate important pulmonary function parameters in lung transplant recipients compared to aerosol placebo and historical control patients. Single-and double-lung transplant recipients may not respond uniformly to treatment, and ongoing randomized trials in lung transplant recipients using ACsA may help elucidate our findings.