High school students who had at least one parent with hypertension (n =22) were compared to schoolmates of the same age with a negative family history of hypertension in the parents (n =21). We investigated in both groups the maximal rate of the ouabainsensitive Na pump and the Na-K cotransport in nystatin-loaded cells and the Lii-Nao countertransport in lithium-loaded cells. The two groups were significantly different only in the sum of net Na transport mediated by the Na-K pump and Na-K cotransport. The mean diastolic blood pressure in the positive family history group was significantly higher. With control for blood pressure the difference in the maximal rate of Na transport was no longer significant; it remains uncertain if control for blood pressure represents 'over-adjustment'. The finding of a higher maximal rate of Na transport in these adolescents who are at increased risk of future hypertension, yet currently well within the normal range, suggests that abnormal sodium metabolism may be a useful marker and appears early in the pathogenesis of this disease.