Cigarette smoke is known to generate active oxygen species such as O2- and H2O2, and contains a variety of irritants capable of reducing the ciliary beat frequency (CBF). While acute cilio-inhibitory action of cigarette smoke no longer needs to be proved, little is known about the contribution of active oxygen compounds in cigarette smoke on the cilio-inhibitory action. Using cultured rabbit tracheal epithelium in vitro and CBF and the time to ciliostasis were measured by a microphoto-oscillation technique. An extract of cigarette smoke was made by bubbling smoke through 5 ml phosphate buffer saline (PBS) for 5 min. Smoke extract alone (a concentration of 10% and 20%) gave ciliostasis after 37 +/- 6 min and 17 +/- 2 min, respectively. Significantly less toxic was smoke extract (a concentration of 10% and 20%) containing 200 micrograms/ml superoxide dismutase (SOD) and 200 micrograms/ml catalase, and the time to ciliostasis were 62 +/- 5 min and 24 +/- 1 min, respectively. There was no significant difference in terms of the time to ciliostasis between 20% smoke extract alone and 20% smoke extract containing inactivated 200 micrograms/ml SOD and 200 micrograms/ml catalase (22 +/- 2 min vs. 23 +/- 3 min). The effect of smoke extract on transcellular transport of fluorescein Dextran through cultured canine bronchial epithelium was also discussed.