Aging causes micro-and macrovascular endothelial dysfunction, as assessed by endothelium-dependent dilation (EDD), which can be prevented and reversed by habitual aerobic exercise (AE) in men. However, in estrogen-deficient postmenopausal women, whole forearm microvascular EDD has not been studied, and a beneficial effect of AE on macrovascular EDD has not been consistently shown. We assessed forearm blood flow in response to brachial artery infusions of acetylcholine (FBFACh), a measure of whole forearm microvascular EDD, and brachial artery flow-mediated dilation (FMD), a measure of macrovascular EDD, in 12 premenopausal sedentary women (Pre-S; 24 +/- 1 yr; (V) over dot(O2max)= 37.5 +/- 1.6 ml.kg (-1).min(-1)), 25 estrogen-deficient postmenopausal sedentary women (Post-S; 62 +/- 1 yr; (V) over dot(O2max) +/- 24.7 +/- 0.9 ml.kg(-1).min(-1)), and 16 estrogen-deficient postmenopausal AE-trained women (Post-AE; 59 +/- 1 yr; (V) over dot(O2max) +/- 40.4 +/- 1.4 ml.kg(-1)min(-1)). FBFACh was lower in Post-S and Post-AE compared with Pre-S women (135 +/- 9 and 116 +/- 17 vs. 193 +/- 21 AUC, respectively, both P < 0.008), whereas Post-S and Post-AE women were not different (P = 0.3). Brachial artery FMD was 34% (5.73 +/- 0.67%) and 45% (4.79 +/- 0.57%) lower in Post-S and Post-AE, respectively, vs. Pre-S women (8.69 +/- 0.95%, both P <= 0.01), but not different between Post-S and Post-AE women (P = 0.3). Post-AE women had lower circulating C-reactive protein and oxidized low-density lipoprotein compared with Post-S women (0.5 +/- 0.1 vs. 1.1 +/- 0.2 mg/l and 40 +/- 4 vs. 55 +/- 3 U/l, respectively, both P = 0.01), but these markers were not correlated to FBFACh (P = 0.3) or brachial artery FMD (P = 0.8). These findings are consistent with the idea that habitual AE does not protect against age/menopause-related whole forearm micro-and macrovascular endothelial dysfunction in healthy nonobese estrogen-deficient postmenopausal women, despite being associated with lower systemic markers of inflammation and oxidative stress. NEW & NOTEWORTHY This is the first study to demonstrate that habitual aerobic exercise may not protect against age/menopauserelated whole forearm microvascular endothelial dysfunction in healthy nonobese estrogen-deficient postmenopausal women, consistent with recent findings regarding macrovascular endothelial function. This is in contrast to what is observed in healthy middle-aged and older aerobic exercise-trained men.