We will measure vascular reactivity after arterial ischemia in two ways, by brachial artery reactivity and by venous plethysmography. Both techniques are sensitive to nitric oxide mediated vascular dilation. Both procedures will be done without the nitroglycerin step. Differences in flow mediated dilation and arterial compliance have been described in the normal menstrual cycle, and should be sensitive to differing biologic effects of estrogen and progestin in the respective contraceptive cycles. We expect that the vasodilatory response to ischemia will represent the net opposing biologic effects of estrogen and progestin, as do the hormone-sensitive plasma proteins. These measurements will be made at day 21 of the second month of each of the three treatment arms, as day 21 is the time of maximum hormone exposure in all three regimens.