Shy-Drager syndrome. Effect of fludrocortisone and L-threo-3,4-dihydroxyphenylserine on the blood pressure and regional cerebral blood flow. In nine cases of Shy-Drager syndrome, the changes in blood pressure and cerebral blood flow on sitting up from a supine position were studied. The influence of fludrocortisone, a synthetic mineralocorticoid, and L-threo-3,4-dihydroxyphenylserine (DOPS), a precursor of norepinephrine, on these changes was examined. On sitting up, the regional cerebral blood flow (rCBF) measured by Xe133 inhalation showed a tendency to decrease. Fludrocortisone reduced the fall of the mean blood pressure significantly. DOPS reduced the fall of both the diastolic blood pressure and rCBF significantly. 