1. The sodium concentration in lymphocytes was measured in a group of 66 normotensive subjects (40 without familial hypertension and 26 with familial hypertension), in a group of 81 patients with essential hypertension and in a group of 14 patients with secondary hypertension.
2. The mean value (±sd) in normotensive subjects with no history of familial hypertension was 21.9 ± 3.1 mmol/kg wet weight, which was significantly lower (P < 0.005) than that of normotensive subjects with familial hypertension (mean value 27.9 ± 4.2 mmol/kg). Lymphocyte sodium concentration was significantly higher in patients with essential hypertension (33.2 ± 3.3 mmol/kg; P < 0.001) than in the subjects with normal blood pressure without familial hypertension.
3. In the patients with essential hypertension there was a significant correlation between lymphocyte sodium concentration and systolic (P < 0.005), diastolic (P < 0.001) and mean (P < 0.001) blood pressure. In the normotensive subjects there was no correlation between the lymphocyte sodium concentration and the blood pressure.
4. The patients with secondary forms of hypertension had normal lymphocyte sodium concentration, except in the case of Conn's disease.
5. Incubation with ouabain increased lymphocyte sodium concentration in the normotensive subjects and patients with essential hypertension; the final sodium concentration was similar in the two groups.
6. When lymphocytes from normotensive subjects without familial hypertension were incubated in plasma of patients with essential hypertension there was an increase in their sodium content.