Inflammation causes epithelial cell sloughing and basement membrane (BM) exposure in canine pulmonary eosinophilia (PE), leading to degradation of the epithelial cell attachment component, laminin-5 gamma2-chain, into small molecular weight fragments. The subsidence of inflammation after treatment down-regulates degradation. Laminin-5 gamma2-chain levels and molecular forms in bronchoalveolar lavage fluid (BALF) were analysed semiquantitatively by Western immunoblotting to compare PE affected (n=20) and healthy dogs (n=16) as well as PE dogs (n=6) before and after corticosteroid treatment. PE dogs expressed significantly elevated levels of total (P<0.01), 36 kDa (P<0.05) and 53 kDa (P<0.05) laminin-5 gamma2-fragments. The 36 Da fragment decreased significantly (P<0.05) after treatment. The laminin-5 gamma2-chain degradation products may be linked to epithelial cell sloughing and BM exposure or healing.