1. Urinary kallikrein was measured in 67 patients with essential hypertension and 25 normotensive subjects variously on unrestricted and low sodium diet. Also, the effect of orally applied hog pancreatic kallikrein on elevated blood pressure and kallikrein excretion was evaluated.
2. Urinary kallikrein was reduced in a large subgroup of patients with sustained essential hypertension.
3. With salt restriction, urinary kallikrein rose markedly in normotensive subjects and patients with borderline hypertension but not in those with sustained hypertension.
4. Oral kallikrein normalized reduced kallikrein excretion and lowered elevated blood pressure.
5. The rise in urinary kallikrein with oral kallikrein was due to an increased formation of endogenous enzyme.
6. A defective kallikrein—kinin system may be involved in both the low urinary kallikrein excretion and the hypertension.