The development and widespread availability of noninvasive testing have revolutionized the approach to the diagnosis of vascular disease. Noninvasive tests are safe, can be performed on an outpatient basis, and are readily repeatable. These tests require skill and experience to perform with acceptable accuracy. In experienced hands, they compare favorably with standard angiography, and, after the initial cost, are less expensive. B-mode ultrasonography provides a gray scale image of the blood vessels. Doppler probes permit analysis of flow patterns and velocity. Color flow imaging, the latest advance, combines high-resolution B-mode and Doppler imaging systems using a computer to provide simultaneous anatomic and physiologic information. This method is a faster and more accurate means of detecting and evaluating the extent of vascular disease. Noninvasive testing is useful in assessing the carotid arteries before vascular or other high-risk operation. Stratification of the risk of future stroke is possible with these tests. This stratification assists in the selection of candidates for carotid surgery among patients with symptomatic carotid disease or asymptomatic bruits in the neck. The hemodynamic significance of obstructive disease in the peripheral arteries can be evaluated and followed by serial noninvasive testing. Noninvasive testing is also of proven value in the surveillance of patients with arterial bypass grafts and in diagnosing local vascular complications of arterial catheterization. Acute and recurrent deep venous thrombosis can be diagnosed accurately by noninvasive testing, greatly reducing the need for venography. In addition, noninvasive testing is particularly suited for screening patients at high risk for developing deep venous thrombosis.