The evolution of our understanding of IL-11 mirrors, in many ways, the problems that are faced by investigators in the post-genome era and the types of techniques that might need to be used to deal with these issues. IL-11 was discovered as a soluble factor in fibroblast supernatants that stimulated the proliferation of "IL-6-dependent" plasmacytoma cells. It was subsequently demonstrated to be an important stimulator of platelet reconstitution and a pleiotropic regulator of nonrespiratory tissues. In the lung, IL-11 is produced by a variety of structural cells and eosinophils in response to a variety of stimuli, including TGF-beta, major basic proteins, and viruses. IL-11 is also detected in exaggerated quantities at sites of virus infection. Its potential effector functions at these sites were defined with constitutive and inducible overexpression transgenic modeling systems which demonstrated that IL-11 causes nodular mononuclear infiltrates, airway remodeling with subepithelial fibrosis, airways obstruction, and airways hyperresponsiveness and can block alveolar development when expressed during development. In accord with these murine findings, IL-11 is selectively expressed in eosinophils and epithelial cells in patients with moderate and severe asthma where expression correlates directly with disease severity and inversely with FEV(1). Studies using transgenic mice also demonstrated that IL-11 inhibits antigen-induced tissue inflammation. Thus IL-11 might be an important regulator of inflammatory and remodeling responses in the asthmatic airway.