Present theory holds that pulsatile pressure of cerebrospinal fluid (CSF) is driven by the force of expansion of the choroid plexus. Alternate theories postulating that a possible movement of the brain is involved in pumping CSF have not, to the authors'' knowledge, been substantiated heretofore. In this study, in vivo, quantitative magnetic resonance (MR) imaging methods were developed to show reproducible magnitudes and directions of CSF flow. Measurements were obtained with a new MR velocity imaging technique at high resolution (0.4 mm/sec), requiring 64 cardiac cycles per image. Twenty-five healthy volunteers and five patients were studied. Observations of pulsatile brain motion, ejection of CSF out of the cerebral ventricles, and simultaneous reversal of CSF flow direction in the basal cisterns toward the spinal canal, taken together, suggest that a vascular-driven movement of the entire brain may be directly pumping the CSF circulation. The authors describe what they believe to be the first observations and measurements of human brain motion, which occurs in extensive internal regions (particularly the diencephalon and brain stem) and is synchronous with cardiac systole.