The aim of this study was to assess clinical signs and altered pulmonary cell expression of cytokines related to eosinophil kinetics in horses with pulmonary eosinophilia. Pulmonary eosinophilia was detected by bronchoalveolar lavage (BAL) in a group of standardbreds in training. Horses had detailed clinical examination, bronchoscopy, endobronchial biopsy and BAL on three occasions at approximately 6 month intervals. During the second sampling period BAL eosinophils were significantly elevated (p>0.010), with five horses having from 5% to 37% eosinophils in BAL. Neither detailed clinical examination parameters nor gene expression of IL-4 and IL-5 mRNA (real-time-PCR) were associated with BAL eosinophilia. Pulmonary eosinophilia abated without treatment apart from deworming. It appears that pronounced lung eosinophilia in horses can be transient, abate without specific treatment, and in this instance, lack correlation to upregulation of expression of either IL-4 or IL-5.