We investigated the bacterial flora and antimicrobial sensitivity in sputum from patients admitted to hospital with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) in order to recommend the best empirical treatment for these patients. The survey was a retrospective study of all patients admitted to Hvidovre hospital with the diagnosis AECOPD during 2004. A total of 118 patients were included. Microscopy, culture and sensitivity testing investigated their sputums. Clinical and paraclinical features were collected from the patients' files. Among the 118 patients, 59 (50%) had a positive sputum culture. The group with positive cultures had a higher blood neutrophil count (p=0.03). There were no other clinical differences between the groups with and without positive sputum culture. The majority of patients with positive sputum cultures were infected with bacteria other than S. pneumonia, mostly H. influenzae and Moraxella catarrhalis. Patients with low FEV(1)<1.0 litre were more likely to be infected with Pseudomonas aeruginosa (p=0.03). The sensitivity patterns of the bacteria showed that the majority were resistant to penicillin. If antibiotics are initiated empirically for AECOPD we recommend either cefuroxime for intravenous treatment or amoxicillin-clavulanate for oral treatment.