This article reviews the data from literature regarding cell sodium and potassium content in young subjects at risk of developing essential hypertension (subjects with family history of hypertension or with borderline hypertension). The studies performed with red blood cells have produced conflicting results: approximately one-half of these studies have found an increase in intracellular Na+ in subjects with family history of hypertension (genetic normotensives) whereas the other studies found no difference. The reasons for these discrepancies are discussed. Studies with leukocytes gave more univocal results and the majority of these studies found an increase in intracellular Na+ in many genetic normotensives. These observations emphasize that it is possible to find a high intracellular Na+ in subjects with normal blood pressure. Longitudinal studies are need to clarify whether subjects with high Na+ are those who will develop hypertension. The data from our studies suggest that subjects with high Na+, even if they are normotensive, exhibit an exaggerated pressor response to mental and physical activities and that a reduction in dietary salt content produces a parallel decrease in intracellular sodium and in pressor reactivity. The data on borderline hypertension are even more scarce than those on genetic normotensives and the different classification criteria produce results which are frequently not comparable. Our studies showed that in borderline subjects not only intracellular Na+ can be increased, but also intracellular K+.(ABSTRACT TRUNCATED AT 250 WORDS)