Even though all human respiratory cilia are similar in structure, they experience a wide range of temperatures between the initial part of the nasal fossae which behave as heat exchangers and the inferior part of the trachea, particularly when we inhale exceedingly cold or hot air. The ciliary beat frequency of ciliated cells from human nasal mucosa and from bronchial mucosa averages 8 Hz when measured at room temperature. In the present study we compared the ciliary beat frequency of human cells from nasal and tracheal mucosa brushings at different temperatures from 5 degrees C to 50 degrees C using two different techniques, ex vivo and in vitro: ex vivo in culture medium less than 24 h after sampling and in vitro after demembranation and reactivation according to a standard procedure developed in our laboratory. Measuring the ATP-reactivated ciliary beat frequency allowed us to check the thermal parameters of the dynein ATPase and all the axonemal machinery. No significant difference in frequency was observed between nasal fossae cilia and tracheal cilia when comparing extreme temperatures in both experimental procedures.