The role of antibiotic therapy in patients with COPD remains controversial. While the outcome of several clinical trials is in favour of antibiotics, the quality of these studies in insufficient. In this study the efficacy of doxycycline is compared to placebo. All concommitant treatment (steroids, bronchodilator therapy, physiotherapy) is standardized.

The investigators hypothesize that patients with an acute exacerbations will have a better outcome when treated with antibiotics.

Inclusion Criteria:

• Acute exacerbation of COPD type I or II according to GOLD
• Ability to perform lung function tests
• Ability to take oral medication

Exclusion Criteria:

• Pregnant or lactating women, or women of childbearing age not using an acceptable method of contraception.
• Pretreatment ( > 24 hours) with an antibiotic for the present exacerbation.
• Pretreatment with corticosteroids (>30 mg for more than 4 days) for the present exacerbation.
• Progression or new radiographic abnormalities on the chest X-ray.
• Severe exacerbation that required mechanical ventilation.
• History of bronchiectasis
• Recent or unresolved lung malignancy.
• Other disease likely to require antibiotic therapy.
• Significant gastrointestinal or other conditions that may affect study drug absorption.
• Class III or IV congestive heart failure or stroke.
• Immunodeficiency disorders such as AIDS, humoral immune defect, ciliary dysfunction etc. and the use of immunosuppressive drugs (>30 mg prednisolone maintenance dose or equivalent for more than 4 weeks).
• Cystic fibrosis
• Tuberculosis.
• Impaired renal function (creatinine clearance < 20 ml/min).