Endothelial dysfunction is an early step in atherosclerosis. The usual method to evaluate endothelial function is ultrasound measurement of the increase in brachial artery mean flow velocity (MFV) and dilatation (BAD) by release of upper arm cuff occlusion. Arm occlusion induces microvascular dilatation, which elicits hyperemia and macrovascular dilation. Differentiating micro from macrovascular dysfunction is therefore problematic in patients such as with diabetes (DM). Passive leg raising (PLR) is an alternative provocation that centralizes blood volume and increases cardiac output resulting in BAD without affecting the downstream microvasculature. We studied 102 subjects with and without diabetes (DM) (42 normal, 60 DM, age 48 19 yrs.). BAD and MFV were assessed with ultrasound both during hyperemia and PLR to evaluate macrovascular function. Laser Doppler Flowmetry (LDF) during both hyperemia and PLR were measured to assess microvascular function. The microvascular and macrovascular responses elicited by the two provocative maneuvers were compared using SPSS statistical software. Among the 42 normal subjects, hyperemia increased BAD (15.4 9.3%, p<.001), MFV (407 301%, p<.001) and LDF (280 286%, p<.001). PLR increased BAD (5.4 3.9%, p<.001) and MFV (24 48%, p1⁄4.007), but did not change LDF (12 53%, p1⁄4.49). Among the 60 DM subjects hyperemia increased BAD (5.96 5.3%, p<.001), MFV (304 287, p<.001) and LDF (222 345%, p<.001). PLR increased BAD (2.1 3.2%, p<.001) and MFV (21 70.7%, p1⁄4.012), but did not change (LDF 4.6 49.6, p1⁄4.12). There was significant correlation between hyperemia LDF and the difference between hyperemia and PLR BAD (r1⁄4.384, p<0.001). The differential effects of the 2 techniques (hyperemia-PLR) was greater for normals versus DM (10.3 9.5 vs 3.9 4.9, p<.001). This suggests a microvascular component to hyperemia but not PLR. In summary, our results suggest that hyperemia induced BAD assess both microvascular and macrovascular function, whereas PLR specifically assesses macrovascular function. Since an impaired BAD response to hyperemia may be due to microvascular or macrovascular dysfunction, PLR carries the potential to assess endothelial dysfunction independent of microvascular disease. The differential effect of the two techniques may be useful to distinguish and quantify microvascular dysfunction. This may have clinical utility in risk stratification and evaluation of therapies in patients with micro and macrovascular disease.