We studied the effects of lactoferrin and lysozyme on ciliary beat frequency (CBF) of rabbit cultured tracheal epithelium by a photoelectric method in-vitro. Lactoferrin (50 mg mL−1) and lysozyme (100 mg mL−1) elicited rapid increases in CBF from 13·3 ± 0·3 to 15·9 ± 0·4 Hz (mean ± s.e., P<0·01) and 13·0 ± 0·4 to 17·2 ± 0·5 Hz (P<0·01), respectively, followed by sustained increases which were maintained at least for 30 min. These effects were dose dependent. The maximal increases from the baseline values (ΔCBFmax) and the concentrations required to produce a half-maximal responses (EC50) were 32·4 ± 5·3% and 14·9 ± 2·8 mg mL−1, respectively, for lactoferrin, and 38·0 ± 4·4% and 2·3 ± 0·3 mg mL−1 for lysozyme. The increases in CBF produced by lactoferrin and lysozyme were not affected by pretreatment of cells with propranolol or Ca2+-free medium. Intracellular cAMP levels remained unchanged after the addition of lactoferrin and lysozyme. These results suggest that lactoferrin and lysozyme stimulate airway epithelial ciliary motility, thereby playing a role in the regulation of mucociliary transport in the respiratory tract.