Molecular mechanisms of COPD exacerbations and the modulating effect of low dose theophylline on that inflammation are elucidated in this project. NF-kappa B-dependent pathway and acetylation status of nuclear histones are to be studied.Design: controlled, prospective and randomized study with or without theophylline, a potent HDAC activator.Objectives: 1) To determine NF-kB activation, histone deacetylase (HDAC) and histone acetyl-transferase (HAT) activity in sputum macrophages and blood monocytes during an episode of exacerbation and 3 months later, once stability is achieved. To correlate these measurements with inflammatory and oxidative stress markers and with pulmonary function and clinical variables. 2) To assess the effect of theophylline on previous molecular, functional and clinical data. Method: 25 patients with COPD will be recruited during an episode of exacerbation requiring hospitalization. NF-kB activation, HDAC and HAT activity, markers of inflammation and oxidative stress will be determined with specific assays. These determinations will be repeated once the patient is stable and compared with smokers and non smoker controls with normal lung function