Background. Failure to decrease blood pressure ( BP) normally during night-time, which is called non-dipping, in hypertensive individuals is associated with higher cardiovascular morbidity and mortality. In addition, non-dipping BP leads to structural changes in the left ventricle; however, the effect of non-dipping BP on coronary flow reserve ( CFR) has not been studied yet. Methods. In this study, we measured CFR of 22 subjects with non-dipper hypertension, and 15 subjects with dipper hypertension using transthoracic second-harmonic Doppler echocardiography ( Acuson Sequoia C256H). None of the subjects had any systemic disease or coronary risk factor except hypertension. Results. Age, gender, body mass index, lipids and echocardiographic findings including left ventricular mass index were similar between the groups. Office BP recordings were similar between non-dipper and dipper groups ( 147.9 +/- 6.1/93.9 +/- 4.3 vs 144.0 +/- 8.0/93.0 +/- 3.7). Daytime and 24-h ambulatory BP measurements were similar within the groups, but night-time BPs were significantly greater in non-dipper group than those were in dipper group. Left ventricular diastolic and systolic functions, and both baseline and hyperemic peak diastolic coronary velocity as well as CFR, were similar between the non-dipper and dipper groups ( CFR: 2.47 +/- 0.59 vs 2.39 +/- 0.47). Conclusion. CFR were similar in patients with non-dipper and dipper hypertension in the absence of excessive left ventricular hypertrophy and other cardiovascular risk factors.