SUMMARY Plasma renin activity is suppressed in approximately 25% of patients with essential hypertension, and the rate of in vitro angiotensin I production after addition of exogenous renin (renin reactivity) is increased in plasma of hypertensive patients. We have recently observed that blood pressure (116 ± 1.5/68 ± 1.7 mm Hg) of young women who had hypertension during a first pregnancy 3-6 years earlier (n = 63) was higher (p < 0.005) than blood pressure (109 ± 1.4/61 ± 1.7 mm Hg) of women who remained normotensive during pregnancy (n = 52). To determine if alterations of the renin-angiotensin axis observed in patients with established hypertension also occur in young adults with relatively high blood pressure, plasma renin activity (PRA), plasma renin concentration (PRC), plasma renin substrate (PRS) and plasma renin reactivity (PRR) were compared in these two groups of subjects. Overall, PRA and PRC were Inversely related to systolic blood pressure (p < 0.02). Excluding women on oral contraceptive agents, the PRA response to standardized treadmill exercise was suppressed (< 1.0 ng/ml/hr) in 19% of women with a history of hypertension during pregnancy and in no women who remained normotensive throughout a previous pregnancy; PRR did not differ [p > 0.8) in the two groups of young mothers (27.1 ng/ml/30 min ± 1.2 SK vs 26.2 ng/ml/30 mln ± 0.9 SE). Thus, renin suppression, but not increased PRR, precedes the onset of hypertension. Oral contraceptive usage was associated with higher systolic blood pressures, increased PRS, and low PRC. Highest blood pressures and lowest PRA occurred in women with a history of hypertension during pregnancy who were taking oral contraceptive agents at the time of study.