The purpose of this study is to compare a combination asthma drug (Symbicort) with its two components, budesonide and formoterol, taken individually or in combination, and with placebo in the long-term maintenance treatment of patients with chronic obstructive pulmonary disease (COPD)

Inclusion Criteria:

• A clinical diagnosis of COPD with symptoms for more than 2 years
• Smoking history of 10 or more pack years
• A history of at least one COPD exacerbation requiring a course of oral steroids and/or antibiotics within 1-12 months before first visit.

Exclusion Criteria:

• A history of asthma
• Patients taking oral steroids.
• Any significant disease or disorder that may jeopardize the safety of the patient