1. Arterial pressure, exchangeable sodium (NaE), exchangeable potassium (KE) and plasma concentrations of sodium, potassium, urea, angiotension II and aldosterone were measured in 34 patients with untreated Conn's syndrome before surgical removal of their adenoma. The study was repeated in 23 patients between 3 and 12 months after the operation.
2. Plasma aldosterone, NaE and plasma sodium concentration were higher and KE and plasma potassium concentration were lower than predicted normal. Surgery corrected these abnormalities, also reducing blood pressure from an average of 183/112 to 138/86 mmHg.
3. Systolic blood pressure was positively correlated with plasma and exchangeable sodium and negatively correlated with plasma potassium concentration. The relation of NaE and arterial pressure was closer in old than in young patients. None of these correlations was significant after operation. Before operation plasma urea was insignificantly related to arterial pressure but after operation a significant and positive correlation emerged.
4. A relation between arterial pressure and NaE is to be expected in a state of mineralocorticoid excess but the different correlation in old and young patients was not expected. A similar difference exists in patients with essential hypertension.