More accurate characterization of coronary artery lesions is needed for evaluation of short and long-term interventions in coronary disease. A method of segmental artery analysis has been developed to maximize the information obtained from coronary arteriograms. Coronary lesions are traced from two projected, perpendicular, 35 mm cineangiographic views and transmetted, in digital form, to a PDP 11/45 computer. Magnification and distortion of the image are compensated for in order to determine the actual vessel profiles, using the catheter and its location as a scaling device. The two views are matched; a spatial representation of the vessel centerline is constructed mathematically; and orthogonal vessel diameters are computed at increments along this centerline. Assuming an elliptical lumen, the absolute and percentage reduction in diameter and cross-sectional area in the stenosis are computed. More complex functions (integrated atheroma mass, Poiseuille resistance, and orifice resistance) are then calculated. The accuracy and variability of the different steps involved in lesion analysis have been determined. Dimensional accuracies of +/- 150 microns (SD) are feasible. Examples are given of patients with Prinzmetal's angina and with progressive coronary disease.