Design and methods. To examine to what extent DI-responses differ between asthma and COPD in adulthood, and whether this is associated with features of airways inflammation and changes in smooth muscle function. 12 Adult patients with asthma and 12 with COPD will undergo single-dose methacholine challenge, with prohibition of DI's or 5 DI's prior to challenge in a cross-over design, measuring airways resistance. On a separate day bronchial biopsies will obtained with immunohistochemistry for inflammatory cell markers, vascularity, microvascular leakage, myosin light chain kinase, NO-synthases, and arginase.