Acute bronchitis and acute exacerbations of chronic bronchitis, common illnesses encountered by general and family physicians, account for approximately 14 million physician visits per year. The pattern of antibiotic prescribing for these infections varies from country to country, but there is no clear rationale for these antimicrobial choices. A recent meta-analysis of all randomized, placebo-controlled trials of patients treated with antibiotics for acute exacerbations of chronic bronchitis concluded that a small but statistically significant improvement could be expected in antibiotic-treated patients. Haemophilus influenzae is the most commonly isolated organism from sputum in patients with acute exacerbations of chronic obstructive lung disease but other Haemophilus species, Streptococcus pneumoniae, and Moraxella catarrhalis may also be found. High-risk patients can be defined as being elderly, with significant impairment of lung function, having poor performance status with other comorbid conditions, having frequent exacerbations, and often requiring oral corticosteroid medication. Well-defined clinical trials measure efficacy of a drug but not the effectiveness in a real world situation. Future studies of new antimicrobials should examine their efficacy in patients with an increased risk of true bacterial infection.