Moxifloxacin, is being tested at approximately 60 study centres in 15 countries to determine if this drug, when taken periodically in addition to the patients normal treatment, is effective at reducing the number of flare-ups of chronic bronchitis he has. Approximately 1132 subjects will participate, and it is expected that the study will run for 2 years in order to reach that goal. The patients individual involvement in the study will be 17 months. Moxifloxacin will be compared to a placebo drug (no active ingredients). The study medication (moxifloxacin or placebo) will be taken in addition to the patients normal medication for chronic bronchitis. In addition to the first clinic visit, called a screening visit, the patient will be required to come back to the clinic for ten more study visits, every 8 weeks. At the first visit the study co-ordinator will provide him with the dates for all the visits. Over a period of 48 weeks the patient will return to the clinic on 6 occasions where he will receive the study medication which he will take for five days, in addition to his normal treatment for chronic bronchitis. After this time the patient will enter a follow up period for 24 weeks, where he will come to the clinic for assessments and continue to take his normal medication but not receive the study drug. A complete medical history will be taken at the first visit, including the patients past and current smoking habit. A breath test will be performed to assess how well his lungs are functioning. In addition, he will also be asked to provide a sputum sample for a microbiological examination to identify any bacteria present in the sample. The patient must be able to provide a sputum sample at the screening visit. If the patient meets all the inclusion / exclusion criteria for the study, he will be allocated randomly to one of the following treatment groups at the second visit.- Treatment group 1: Receives moxifloxacin orally once daily for five days.- Treatment group 2: Receives a matching placebo once daily for five days.In between each visit (four weeks after your clinic visit), the study site co-ordinator will contact the patient to check on his well being. If the patient or the doctor decides to stop the patients participation in the trial for any reason, the patient will be required to return to the clinic for a physical examination, take a breath test, provide a sputum sample (if possible) and have a blood sample taken.

Inclusion Criteria:

• Male or female out-patients >/= 45 years
• Subjects suffering from chronic bronchitis
• FEV1\