The development of a subselective coronary Doppler catheter coupled with pharmacologic coronary resistance vessel vasodilation has enabled clinicians to assess coronary vasodilator reserve in humans. This technique has proven useful in the clinical management of patients with a variety of cardiologic problems. This review describes usefulness of Doppler measurements of coronary flow reserve for (1) functional assessment of coronary stenoses of intermediate severity; (2) determination of the need for lesion-specific interventional therapy; (3) assessment of the severity of saphenous vein bypass graft and graft-native vessel anastomotic lesions; (4) assessment of the coronary microcirculation.