The synthesis of P-glycoprotein 170 (P-gp), a “multidrug resistance” protein capable of extruding various drugs including 11-OH steroids from human cells, can be upregulated by certain glucocorticosteroids. This study demonstrates the presence of P-gp in the columnar surface epithelium and in glandular acini of healthy nasal mucosa with immunohistochemical technique. Furthermore, nasal polyps from 5 of 17 patients treated with clinical doses of a topical nasal steroid, budesonide, appear to show a stronger staining intensity for P-gp than polyps from 13 untreated patients. This suggests the possibility of local P-gp gene induction by topical glucocorticoid treatment. Upregulation of P-gp synthesis appears as a new possible cause of relative resistance to topical steroid medication in patients with nasal inflammatory disease.