1. Prostaglandin-dependent, frusemide-induced changes in renal plasma flow, glomerular filtration rate and plasma renin activity were measured in 14 patients with mild essential hypertension.
2. The renal haemodynamic responses to frusemide were the same as in 10 normal subjects.
3. Frusemide-induced changes in urinary PGE and kallikrein excretion were also the same as in normal subjects.
4. Impaired renal release of vasodilator prostaglandins in essential hypertension is likely to be secondary to the hypertension rather than an underlying factor in its development.