Young women who became pregnant as adolescents and developed hypertension during their first pregnancies had higher blood pressures than women who had remained normotensive throughout pregnancy. These young mothers served as subjects for a study to evaluate the relationship between different levels of "normal" blood pressure and renin-aldosterone. Overall, plasma renin activity (PRA), but not plasma aldosterone, was inversely related to systolic blood pressure both before (r = -0.28; p less than 0.003) and after (r = -0.24, p less than 1.01) treadmill exercise. Unrelated to blood pressure, PRA was also lower in blacks and in women using oral contraceptive agents (p less than 0.01). Of women with a history of hypertension in pregnancy, 30% (9 of 30) had low PRA after exercise. Low renin was associated with higher blood pressures. At the time of a second exercise test 3 years later, these women still showed elevated arterial pressure and low renin. PRA was also suppressed in the children of mothers with low renin, and there were significant correlations between maternal and child PRA (r = +0.55; p less than 0.003) and between maternal and child aldosterone (r = +0.60; p less than 0.001). In conclusion, low renin may be an appropriate response to higher arterial pressures, and within families may be a marker of "pre-hypertension."