['To test whether a reduction in air temperature within the clinical range [37 degrees C to 30, 100% relative humidity (RH)] altered mucus transport velocity (MTV) and ciliary beat frequency (CBF) in an in vitro ovine tracheal model.', 'Controlled laboratory study.', 'University research laboratory.', 'Farm-reared sheep.', 'Tracheae were mounted flat in an organ bath. Krebs Henseleit bathed the serosal surface and air at 100% (RH) was passed over the mucosal surface at 4 l/min. Cilial beat frequency (CBF) was measured photo-electrically and mucus transport velocity (MTV) by timing movement. After 2 h at 37 degrees C (100% RH) the tissue was either maintained with those settings (controls), or the air temperature reduced to 34 degrees C or 30 degrees C. Tissue was taken for histology before and after each experiment.', 'CBF was 19.8+/-2.7 beats/s and MTV 5.7+/-2.6 mm/min in tissue exposed to air at 37 degrees C. Cilial activity continued for up to 6 h in the controls but mucus transport was more fragile. Reduction of the air temperature to either 34 degrees C or 30 degrees C led to a decrease in both CBF and MTV and, frequently, total mucociliary failure. There was a reduction in epithelial mucous cell numbers in all preparations. Tissues exposed to low temperature had additional abnormal histology.'] Does mucociliary function deteriorate in the clinical range of inspired air temperature and humidity?