The aim of this study was to assess whether moxifloxacin is able to inhibit the synthesis of and to disrupt biofilms produced in vitro by bacterial pathogens involved in acute bacterial exacerbations of chronic bronchitis. Three strains each of Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, Staphylococcus aureus and Escherichia coli recently isolated from clinical respiratory specimens and capable of slime production were used. Biofilm formation on polystyrene plates was quantified spectrophotometrically by established methodologies. Moxifloxacin (0.5 mg/L) inhibited slime synthesis by >70% in S. aureus, H. influenzae and S. pneumoniae, 45-70% in E. coli and 35-70% in M. catarrhalis. Disruption of pre-formed structures was also promoted by moxifloxacin both for initial (5h) and mature (48 h) biofilms. Drug concentrations reached during therapy (0.5-4 mg/L) resulted in a breakdown of initial biofilm of 60-80% in H. influenzae and S. pneumoniae, 48-86% in S. aureus, 37-69% in M. catarrhalis and 51-71% in E. coli. Mature biofilms were less susceptible to degradation. Moxifloxacin at concentrations that can be achieved in the bronchial mucosa during therapy therefore promotes a significant inhibition of biofilm synthesis and induces slime disruption, a feature that may be instrumental in reducing the exacerbations so frequently observed in this condition.