Background: Allergic eye disease, in some form, affects greater than 20 million people in the US. No systematic investigation has been undertaken to attempt to understand the molecular signaling events on the ocular surface and to explain the mechanism and course of cellular infiltration in allergic eye disease patients. Purpose: To determine if activated human conjunctival mast cells will supply sufficient cytokines and other mediators to initiate and direct a well orchestrated trafficking of eosinophils to the ocular surface, facilitate their adhesion, and cause their release of potent affecters of ocular surface damage. Secondly, to determine the differences in molecular signaling in patients undergoing seasonal allergic conjunctivitis compared to those with sight threatening disease such as Atopic Keratoconjunctivitis. Methods: Following activation with anti-IgE or secretagogue, human conjunctival mast cell release of cytokines will be evaluated by ELISA, RT-PCR, or micro bead assay. Following treatment with activated supernatants from conjunctival mast cells (identifying important cytokines using blocking antibodies), human conjunctival or corneal epithelial cells, will be evaluated by FACS, RT-PCR, and ELISA for production of cell adhesion molecules and eosinophil attracting chemokines. Eosinophil adhesion to these stimulated epithelial cells will be measured by eosinophil peroxidase adhesion assays. Following their attachment to epithelial cells, eosinophils will be measured for activation by evaluation of oxidative burst and for release of potent affecters of epithelial cell damage such as eosinophil cationic protein by ELISA. These in-vitro results will guide our in vivo evaluation (FACS, RT-PCR) of ocular surface cells (obtained by impression etiology) of patients undergoing an allergic reaction induced by topical provocation with allergen. Conclusion: We will be able to connect the molecular signaling events of cells of the ocular surface to the known pathologic findings of allergic eye diseases. This understanding will allow the development of precise strategies for intervention.