Melatonin, a natural hormone of the pineal gland exclusively released during the dark phase, exhibits vasodilatatory effects in distal skin regions and reduces core body temperature. This study investigates whether exogenous melatonin (5mg p.o. at 2p.m.) in the afternoon, when no endogenous melatonin is secreted, increases not only distal skin blood flow, but also choroidal blood flow and changes oxygen consumption. Two subject groups were studied, women with vasospastic syndrome (VS) and controls. The main hypothesis is: melatonin normalizes distal vasoconstriction in VS.