In order to examine fluticasone propionate's mechanism of inhibiting nasal allergic symptoms, topical dosing of FP to patients with Japanese cedar pollinosis was started before the pollen scattering season, and the kinetics of basophilic cells and eosinophils which infiltrated into the surface of nasal mucous membrane were observed. Patients with Japanese cedar pollinosis were divided into two groups. Before and in the early period of the pollen scattering season, one group received FP and the other group a placebo, topically into the nostrils. In the mid and late season, both groups were treated with FP topical dosing. The study was carried out in the double blind manner. In the pre-, early and late season, specimens were scraped from the nasal mucosal surface, basophilic cell and eosinophil counts in the specimens were measured, and histamine and ECP contents in the specimens were also determined. Topical use of FP starting pre-season significantly inhibited symptoms of Japanese cedar pollinosis, as well as accumulation of basophilic cells and eosinophils in the nasal mucosal surface. Histamine and ECP contents in the nasal specimens tended to decrease with the topical use of FP.