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Women using oral contraceptives have higher ambulatory blood pressures (BPs) than other women. We sought to learn whether this was associated with an alteration in the balance of angiotensin II (Ang)/Ang (1–7) and whether this ratio and BP remained constant throughout the menstrual cycle.In total, 30 (15 ovulatory, 15 taking oral contraceptives) healthy, normotensive women aged 18–30 years were studied. The ovulatory group was assessed within days 1–5 (follicular phase) and 19–23 (luteal phase) and the oral contraceptive group within days 19–23. Peripheral, central and 24-h BP, vascular wall stiffness, and body composition were measured along with plasma estradiol, progesterone, renin, aldosterone, Ang II, and Ang (1–7) concentrations.In ovulatory women plasma renin activity (P < 0.001), renin concentration (P < 0.01) and aldosterone (P < 0.05) were higher in the luteal than follicular phase, whereas BP, Ang II and the Ang II/Ang (1–7) ratio remained constant. In women taking oral contraceptives, plasma renin activity (P < 0.001) and concentration (P < 0.01) were higher than in follicular phase ovulatory women whereas 24-h BP, Ang II, Ang (1–7), and the Ang II/Ang (1–7) ratio (P < 0.01) were higher than in both phases of the ovulatory group. However, there was no significant correlation between BP and the Ang II/Ang (1–7) ratio.This study confirms that BP is constant throughout the normal menstrual cycle along with a constant balance between the vasoconstrictor (Ang II) and vasodilator [Ang (1–7)] arms of the renin–Ang–aldosterone system. Women taking oral contraceptives have a higher Ang II/Ang (1–7) ratio associated with their BP elevation although no causal relationship has been found.