BACKGROUND Although earlier studies demonstrated endothelial dysfunction and systemic inflammation in patients with microvascular angina (MVA), the correlations between flow-mediated dilation (FMD), high-sensitivity C-reactive protein (hsCRP) levels and Duke treadmill score (DTS), a comprehensive index representing the severity of ischemia, have not been elucidated in this setting. OBJECTIVE To explore the possible relationships among brachial FMD, serum hsCRP levels and DTS in MVA patients. METHODS AND RESULTS A total of 89 subjects with chest pain and a normal coronary angiogram were studied. The exercise treadmill test (ETT) was performed using the Bruce protocol for calculating the DTS. Brachial FMD and serum hsCRP levels were measured. The mean (± SD) brachial FMD was 5.45±2.24% in the group with positive ETT and 8.19±2.78% in the group with a negative ETT (P<0.001). Mean serum hsCRP levels were significantly higher in the group with positive ETT than in the group with negative ETT (4.93±1.63 mg/L versus 3.41±1.65 mg/L; P<0.001). Brachial FMD and serum hsCRP levels showed significant differences among the three groups according to DTS risk stratification. The DTS was positively correlated with FMD (r=0.532; P<0.001) and negatively correlated with hsCRP level (r= 0.461; P<0.001). CONCLUSIONS Brachial FMD and serum hsCRP levels may be associated with DTS in patients with MVA.