We measured components of the cerebrospinal fluid renin-angiotensin system from patients with essential hypertension under different dietary sodium intakes. The cerebrospinal fluid concentration of angiotensin II (Ang II) from the patients on a normal-sodium diet was 1.36 +/- 0.41 fmol/ml (n = 5). Neither the inactive nor the active form of renin was detected by the enzymatic activity or by the immunoreactivity, whereas angiotensinogen was detected (38.6 +/- 3.1 pmol/ml, n = 5). The Ang II level remained unchanged even after incubation of the cerebrospinal fluid at 37 degrees C for 3 h. Further, when authentic Ang II was added to the cerebrospinal fluid followed by incubation for 3 h at 37 degrees C, more than 90% of the added Ang II remained unchanged. Thus, the cerebrospinal fluid Ang II level may be reflected by the activity of the brain Ang II-forming system, as it was not affected by the cerebrospinal fluid constituents. The circulating renin-angiotensin system was stimulated by sodium depletion, and the cerebrospinal fluid concentration of Ang II also increased significantly. Sodium depletion may stimulate the brain Ang-II forming system, as it does the circulating renin-angiotensin system.