The frequency spectrum and the amplitude transfer function from arterial pulse pressure to the CSF pulse wave were estimated in the lateral ventricle, cisterna magna and lumbar subarachnoid space of anaesthetised ventilated cats under various conditions: (a) normal status, (b) inhalation of 5% CO2 and (c) saline infusion into the CSF space (0.045 ml/min). The CSF pulse waveforms in the lateral ventricle and cisterna magna were almost identical in all conditions. Inhalation of CO2 and saline infusion increased the values of the amplitude transfer function from blood pressure to the CSF pulse wave in the lateral ventricle and cisterna magna to a similar extent. The CSF pulse in the lumbar sac was remarkably damped under both normal conditions and during CO2 inhalation, but the damping was diminished by saline infusion. During the saline infusion, the spinal canal appeared to function as a low-pass filter to the conduction of the CSF pulse.