To understand the mechanism of the effect of estrogen on nasal mucosal hyperreactivity, animal models (guinea pigs) with different levels of estradiol (E2) were observed as follows: 1. effect of the change of E2 levels on E2 receptors (E2R) content in nasal mucosa; 2. effect of E2 level changes on histamine content in nasal mucosa and on nasal mucosal eosinophil and mast cell counts; 3. effect of E2 on release of cytokine IL-6 from macrophages. The results showed that high level of E2 might reduce the E2R content and eoinophil count but no significant effect on mast cells count and histamine content. The secretion of IL-6 from the macrophages was suppressed by E2 within concentration range of 3.13-50 micrograms/L. It was suggested that estradiol may play a complicated role in nasal mucosal hyperreactivity.