Proteoglycans are a family of structurally distinct, polyanionic complex carbohydrates composed of repeating disaccharide units. Proteoglycans include heparin, heparan sulphate, chondroitin 4-sulphate, chondroitin 6-sulphate, dermatan sulphate, and hyaluronic acid. Heparin is found in the granules of a subset of mast cells where it is bound to various mediators including histamine. Heparan sulphate has a much wider distribution in the body, being associated with stromal matrices, basement membrane and many cell surfaces, particularly the surface of endothelial cells. Heparin is an anticoagulant, but it is now very apparent that it possesses many other biological activities that have relevance to our understanding of lung diseases, particularly inflammatory diseases of the airway. Recent evidence suggests in the airway when administered by inhalation that could be exploited therapeutically.