Ciliary beat frequency (CBF) in various parts of brain ventricular system, as well as in trachea of hamsters, was examined. Coronal sections of brain and tracheal rings were maintained in a thermostatically controlled perfusion chamber and CBF measured by a photoelectric system equipped with a fiber-optic probe. CBF (Hz) values of lateral ventricle, aqueduct and fourth ventricle were 27.9 +/- 4.6; 30.7 +/- 7.7 and 31.9 +/- 7.8 Hz, respectively. CBF in the third ventricle--19.8 +/- 7.1 Hz--was significantly lower than in other segments of ventricular system. CBF in choroid plexus cilia was very slow, 5-10 Hz, whereas in tracheal rings amounted to 13.7 +/- 3.1 Hz. Bovine cervical mucus and mucus stimulant reversibly inhibited CBF in brain but not in trachea. Brain cilia in contrast to those in trachea were not capable of transporting particles. In addition to demonstrating differences between tracheal and ependymal cilia, this work suggests that cilial motility plays a functional role in local mixing of cerebrospinal fluid, but does not relate to the bulk flow within the ventricular system.