Using a chronically implanted telemetric pressure sensor, we have determined the quantitative relationship between changes in body position and ventricular fluid pressure in normal subjects and subjects with shunts. The method allows accurate, reliable measurement of negative as well as positive pressures. We describe the derangement of postural intraventricular pressure regulation caused by placement of a shunt, as well as the influence of various shunt systems and the antisiphon device on this problem. Ventriculoatrial, ventriculoperitoneal, and ventriculopleural shunts all caused similar severely abnormal postural intracranial pressure relationships. The antisiphon device was generally effective in restoring normal pressures in patients in the upright position. We discuss the implications of our findings for understanding the mechanisms of postural intracranial pressure regulation in patients without hydrocephalus.