The molecular biologic events in the development of nasal polyps are now becoming unraveled. It appears that eosinophils are the dominant inflammatory cell present in this tissue. The events leading up to the extravasation of eosinophils into the lamina propria nasal polyps are regulated by the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-1 beta. These cytokines upregulate very late antigen-4 on the surface of eosinophils and vascular cell adhesion molecule-1 on the surface of the endothelial blood vessel. Chemokines such as RANTES (regulated upon activation, normal T-cell expressed and secreted) and eotaxin are responsible for the movement of eosinophils into the lamina propria of the nasal polyp. The release of major basic protein has an effect on alteration of the epithelial architecture and on the sodium and chloride flux into and out of the apical epithelial cell of the tissue. Finally, the alteration of the surface epithelium results in a defect in the migration of the cystic fibrosis transmembrane regulator protein to the apical surface. These two events, the release of major basic protein from the eosinophil and the alteration of the architecture of the surface epithelium, lead to an increase in sodium absorption and resultant edema: the hallmark of the pathology of the nasal polyp.