The mucociliary escalator is the first line of defence of the upper and lower respiratory tracts (Greenstone and Cole, 1985; Sleigh et al., 1988). Failure of mucociliary clearance is associated with chronic or recurrent respiratory tract infection. Ten patients with chronic rhinosinusitis underwent nasal brushings for the assessment of ciliary beat frequency. In two no beating cilia were seen; in the remainder the mean value was 9.3 Hz +/- 2.3; range 6.1-12.8 Hz (n = 8). Following three months continuous oral antibiotic therapy repeat nasal brushings demonstrated increased ciliary beat frequencies in all patients, mean value 13.7 Hz +/- 1.6; range 11.5-16.3 Hz (n = 10); (p < 0.01; paired t-test). Depression of mucociliary clearance can occur secondarily to chronic infection and is improved by prolonged antibiotics.