The effects of corticosteroids on tracheal mucociliary transport (MCT) were examined in pigeons. Intramuscular administration of corticosterone had no effect at 1.0 mg/kg, while at a larger dose of 5.0 mg/kg, it slightly, but significantly increased the MCT rate. Metyrapone significantly decreased the MCT rate, and the inhibitory action was blocked by 1.0 mg/kg corticosterone. The present study suggested that corticosteroids modulated the mucociliary clearance, especially under some diseases associated with a decreased level of endogenous corticosteroids.