1. In patients with essential hypertension plasma renin concentration (PRC) was assessed in relation to age, plasma volume, extracellular fluid volume, aldosterone secretion rate, renal vascular resistance, filtration fraction and excess sodium excretion after acute salt loading.
2. Up to a calculated renal vascular resistance of 20 000 dyn s cm−5, PRC was found to be inversely related with the above-mentioned variables except plasma volume, extracellular fluid volume and aldosterone secretion rate.
3. It is concluded that the phenomenon of renin suppression is not dependent on mineralocorticoid excess. Instead, a decrease in PRC together with hypernatriuresis appears to reflect a progressive switch in intrarenal haemodynamic relationships. Renin suppression should therefore be considered to be a feature of progressive, but still uncomplicated, essential hypertension.