1. The 24 h urinary excretion of kallikrein has been studied in 40 normotensive control subjects and in 74 age-matched patients with essential hypertension under similar conditions. By use of the renin-sodium index, hypertensive patients were divided into two subgroups: low-renin hypertension and normal-renin hypertension patients. Urinary kallikrein determinations were also obtained from six hypertensive patients with primary aldosteronism.
2. Urinary kallikrein was significantly lower both in patients with normal-renin and low-renin essential hypertension. Urinary kallikrein excretion was very high in the patients with primary aldosteronism.
3. In nine hypertensive patients β-adrenoreceptor-blocking therapy caused a significant decrease of plasma renin activity, but had no significant effect on urinary kallikrein excretion.
4. The results support the concept that low urinary kallikrein is likely to be a marker of essential hypertension. Under certain conditions its excretion is positively related to mineralocorticoid hormone concentrations but it is not primarily related to the renin-angiotensin system.