Cerebrospinal fluid (CSF) flow in the cerebral aqueduct and spinal canal was analysed using real-time magnetic resonance imaging measurement techniques. Respiration-induced rhythmic modulation of the cardiac-related oscillating CSF pulsation in the cerebral aqueduct and spinal canal was found. Deep inspiration was immediately followed by a marked increase in downward CSF flow in the cervical spinal canal, whereas a delay of about two heart beats was seen before downward flow from the third to the fourth ventricle increased. This pattern was also detected during yawning and was followed by a marked increase of blood flow in the internal jugular vein.