Rhinoconjunctivitis caused by pollen allergy is characterized by typical signs and symptoms and mucosal infiltration by inflammatory cells during pollen season. It has been recently demonstrated that the adhesion molecule system is deeply involved in cell-to-cell interaction during inflammatory response consequent to allergic reactions. The aim of this study was to evaluate the expression of intercellular adhesion molecule-1 (ICAM-1 or CD54) on nasal epithelial cells, before and during natural seasonal exposure, in 10 allergic patients (Parietaria judaica-sensitized) and in 10 healthy volunteers, correlating this parameter with clinical and cytologic involvement. Nasal epithelial cells of allergic subjects showed a significant expression of CD54 during pollen season (p < 0.001). On the contrary, no CD54 expression was observed out of pollen season. In healthy volunteers no CD54 expression was observed both before and during pollen season. Cytologic evaluation demonstrated an infiltration by eosinophils (mainly activated [EG2+]), (p < 0.001), neutrophils (p < 0.001), and metachromatic cells (p < 0.001) during pollen season only in allergic subjects. Therefore results indicate that seasonal allergic rhinitis is characterized by an infiltration of inflammatory cells correlated with CD54 expression on nasal epithelial cells. This phenomenon is specific, being restricted only to allergic patients during pollen season.