Cyclic AMP elevating agents have been shown to exhibit anti-inflammatory properties in addition to functions such as bronchodilation. The aim of this study was to investigate this dual action of clenbuterol (CB; Ventipulmin) on horses affected with recurrent airway obstruction (RAO). Seven RAO susceptible horses received inhalation challenges with aerosolised lipopolysaccharide (LPS), hay dust suspension (HDS) and Aspergillus fumigatus antigen (AF) with and without prior treatment with intravenous CB. Data showed that CB exerted significant beneficial effects on lung function, total cell count (TCC) and bronchoalveolar lavage neutrophil influx. In addition, CB significantly decreased the expression of several pro-inflammatory cytokines and chemokines in the alveolar macrophages of RAO-susceptible horses after challenge with LPS and HDS, and increased the expression of interleukin-6, known to act as a pro-and anti-inflammatory cytokine, following different challenges. This anti-inflammatory activity of CB is of additive value to its currently recognised use in equine RAO.