The expectorant activity of naringenin was studied. Mucus secretion was evaluated in mice by measuring the tracheal output of phenol red. Mucociliary movement function was investigated using a migration method of carbon granules in unanesthetized pigeons. And the effect of naringenin on the secretion of mucin and lysozyme was performed in the rat tracheal ring explants. Naringenin could significantly increase the secretion of phenol red from mouse tracheas at the doses of 30-67 mg/kg (i.g.) (P<0.05). Naringenin, at the dose of 90 mg/kg, increased the tracheal mucociliary velocity (TMV) to 144.4% of control (P<0.01). 100 microM naringenin could enhance the basal lysozyme secretion, but had no effect on the basal mucin secretion from the rat tracheal ring explants. Treatment with naringenin at higher concentration (10 micromol/l) could inhibit the 100 ng/ml lipopolysaccharide (LPS)-induced mucin increase. These data suggest, therefore, that naringenin has the expectorant activity.