1. Intralymphocytic sodium concentration was measured in 50 patients with essential stable hypertension, 44 patients with labile hypertension and 40 subjects with normal blood pressure.
2. Intralymphocytic sodium concentration in normotensive subjects was significantly lower than in the other two groups.
3. The concentration was significantly correlated with mean blood pressure in the group as a whole and in the groups with stable and with labile hypertension. No correlation was found in normal subjects.