Plasma renin activity (P.R.A.) and plasma aldosterone (P.A.) were studied basally and after various stimuli in eight diabetic subjects with orthostatic hypotension and autonomic neuropathy. Five of them had chronic renal failure and proteinuria. On a diet containing 100 mEq Na/24 H, mean P.R.A. was 0,80 +/- 0,32 ng/ml/h in the supine position and 0,95 +/- 0,43 ng/ml/h in the upright position (N.S.); mean P.A. was 111 +/- 77 pg/ml in the supine position and 234 pg/ml in the upright position (p less than 0,01). On a diet containing 10 mEq Na/24 H, mean P.R.A. was 1,54 +/- 0,76 ng/ml/h in the supine position and 2,44 +/- 1,53 ng/ml/h in the upright position (N.S.). There was little stimulation of P. R. A. by low sodium intakes. After furosemide (n = 6), epinephrine + norepinephrine (n = 4) or diazoxide (n = 2), there was no stimulation of P.R.A. and P.A. Thus in diabetic patients with orthostatic hypotension and autonomic neuropathy basal values of P.R.A. and P.A. are in the normal range but there is dysregulation of renin-angiotensin-aldosterone system.