1. The haemodynamic response to antagonistic (10 μg min−1 kg−1) and agonistic (40 μg min−1 kg−1) doses of saralasin was studied in young essential hypertensive patients. Blood pressure behaviour alone was thought to be inadequate to describe the response pattern.
2. Pre-saralasin setting of the renin-angiotensin axis was varied with salt intake (15 and 290 mmol of Na+/day) each for 10 days. This failed to influence blood pressure or plasma volume.
3. Antagonist blockade after low salt lowered blood pressure in three patients with the highest plasma renin values. Cardiac output rose in two of these, but it dropped in all others.
4. Decreases in cardiac output occurred with both doses of saralasin and even with suppression of the renin-angiotensin axis. This response is therefore unlikely to be due to removal of myocardial or venous angiotensin effects.
5. The renin-angiotensin system played a part in maintenance of blood pressure only with severe salt restriction and in a small proportion of cases.
6. No heart rate effect was seen with saralasin.
7. Blood pressure and total peripheral resistance responses were dependent on pre-(antagonist/ agonist) setting, but heart rate and cardiac output were not influenced by this factor.