Normotensive young men with family histories of hypertension gain weight and decrease their intraerythrocyte sodium content during a 5-year follow-up. Young normotensive men matched for age and body mass index with (n = 16) and without (n = 13) family histories of hypertension were investigated at baseline and after 5 years of follow-up with respect to blood pressure, body weight and intracellular sodium content. Subjects with positive family histories of hypertension increased significantly in body weight (from 81.9 +/- 11.5 kg to 89.5 +/- 11.4 kg, P less than 0.001) compared to subjects with negative family histories of hypertension (from 79.9 +/- 10.8 kg to 80.7 +/- 12.2 kg, NS). Their blood pressure did not differ initially (137 +/- 12/75 +/- 11 mmHg vs. 135 +/- 8/72 +/- 9 mmHg), but was reduced in subjects without family histories of hypertension (to 125 +/- 3/68 +/- 13 mmHg) in the follow-up examination. At follow-up, body mass index showed a positive correlation with blood pressure among subjects with positive family histories of hypertension (r = 0.77, P less than 0.001). At baseline, subjects with hypertensive fathers had significantly higher intraerythrocyte sodium levels than subjects with normotensive parents. At re-examination 5 years later, this difference was no longer present. We conclude that normotensive subjects with positive family histories of hypertension are predisposed to gain weight rather than to show an increase in blood pressure at this age. Normalization of intracellular sodium content, as found in the present study, could be a consequence of this weight gain and the ensuing metabolic adaption. 