Exposure to mild degrees of lower body negative pressure (between atmospheric and 40 mm Hg below atmospheric) caused a transient reduction in hand blood flow. Greater reductions in lower body negative pressure (40 mm Hg or more below atmospheric) led to a more sustained reduction in hand blood flow. This sustained response to LBNP is unlike the reflex effects on hand blood flow caused by tilting into the foot-down position. The possibility that the response is the result of several different stimuli is discussed.