The effect of interleukin-5 (IL-5) on intercellular adhesion molecule-1 (ICAM-1) gene expression in human nasal mucosa was studied using the method of gene expression quantification. Recombinant human IL-5 was shown to induce ICAM-1 gene expression in the nasal mucosa of patients with nasal allergy, but not in the mucosa of non-allergic patients. The peak level of ICAM-1 gene expression was seen 6 h after IL-5 stimulation. In the nasal mucosa of patients with nasal allergy, IL-5 might act not only as an eosinophil chemotactic factor, but also as an enhancement factor for the expression of adhesion molecules, thereby accelerating eosinophil appearance. The results also suggest that the nasal mucosa of patients with nasal allergy somehow favors adhesion molecule induction by IL-5.