Human nasal cilia were perfused with aqueous solutions of two corticosteroid aerosols, beclomethasone dipropionate (BPD) and flunisolide, with the main preservative of flunisolide, propylene glycol, and with placebo. The concentration used were BPD 0.1 mg/ml, 0.05 mg/ml, 0.005 mg/ml and 0.0005 mg/ml, flunisolide 0.25 mg/ml, 0.05 mg/ml, 0.025 mg/ml and 0.00025 mg/ml, and propylene glycol 20 mg/ml and 200 mg/ml. A dose-related decrease in ciliary beating frequency (CBF) was seen after perfusion with both BDP and flunisolide as well as propylene glycol. The decrease in CBF following perfusion with propylene glycol was partially reversible upon re-perfusion with medium alone, whereas the decrease seen after BDP and flunisolide was irreversible. Although previous studies have shown no adverse effect on the mucous membrane except for the areas hit by the impact of the sprays, our results suggest that caution should be taken when the dose and/or the length of treatment is considered, and that the effect of administration of these drugs on CBF in vivo needs to be investigated.