To study the detailed effects of exogenous adenosine triphosphate (ATP) on ciliary function, we used the differential interference microscope equipped with high speed video and evaluated ciliated cells from the human sinus mucosa in monolayer culture. With this system it was possible to evaluate all parts of ciliary motility with a minimum of interference from the mucous membrane, secretory cells and the autonomic nervous system. The best direct ciliostimulative effect of exogenous ATP on ciliary beat frequency (CBF) and ciliary beat amplitude (CBA) was observed at concentrations of ATP ranging from 10(-5) M to 10(-3) M. Exogenous ATP appeared to normalize the slightly damaged ciliary motility in groups with an initial CBF of 14 Hz or higher. When the CBF was less than 14 Hz, ATP produced an increase in CBF greater than 40%, an increase in CBA greater than 30%, but these did not reach the normal level in 5 min. The biggest increases: 59.9% in CBF and 40.7% in CBA were seen in the group with an initial CBF less than 9 Hz. In the cells with a low initial CBF and unsynchronized motility exogenous ATP increased the synchrony of ciliary movement together with an increase in CBF and CBA.