1. This study has confirmed that serum from patients with essential hypertension inhibits sodium transport and elevates intracellular sodium in normal human leucocytes in vitro when compared with that of well matched normotensive controls.
2. The magnitude of this effect was positively correlated with the diastolic blood pressure of the hypertensive patient.
3. The degree of sodium transport inhibition conferred by the hypertensive's serum was correlated with the abnormal sodium transport in the hypertensive's own leucocytes.
4. These results confirm the presence of a serum inhibitor of sodium transport in essential hypertension. The relationship between the inhibitory effect and severity of hypertension argues that it may be of mechanistic importance.