Brachial artery reactivity noninvasively tests endothelial function. Cuff pressures of 180 to 300 mm Hg have been used. These pressures are ill advised in neonatal and premature infants. We therefore evaluated the use of substantially lower occlusive pressures. Fifteen adult subjects were enrolled. One arm was occluded to 200 mm Hg, and the other arm was occluded to 40 mm Hg above the resting systolic pressure. The occlusion time was 4.5 minutes. The brachial artery was measured at baseline and 1 minute after cuff deflation. Low pressure occlusions averaged 155.7 +/- 7.8 mm Hg versus 200 mm Hg for high pressure occlusions (P <.0001). One of 15 patients with low pressure occlusions reported discomfort versus 7 of 15 with high pressure occlusions (P <.05). Brachial artery reactivity increased by 8.0% +/- 2.5% with low pressure occlusions versus 7.5% +/- 2.7% with high pressure occlusions (P = not significant). Brachial artery reactivity can be assessed at lower occlusive pressures. This may extend the applicability of the technique to children and neonates.