This study defines the effect of artificial surfactant on ciliary beat frequency. We employed guinea pig tracheal rings and a photomultiplier which allows in vitro measurement of ciliary beat frequency. The beat frequency without surfactant decreased continuously while surfactant caused a relative increase in beat frequency. The difference between the relative beat frequency in the presence and absence of surfactant was significant. The effect of surfactant was dose dependent. Fifteen minute treatments with 2 mM hydrogen peroxide reduced the beat frequency. The reduction partially recovered in the absence of surfactant. In contrast, surfactant markedly accelerated the recovery of the beat frequency. Surfactant did not influence the effect of terbutaline (a beta 2-adrenergic agonist) on beat frequency. These results indicate that artificial surfactant can, in some circumstances, promote ciliary beat frequency. This concept is important to the clearance mechanism of the airways, and its application to some pathophysiological states such as chronic bronchitis and bronchial asthma should be considered.