Rapid and accurate assessment of coronary artery stenotic severity is important in therapy and understanding of coronary artery disease. Since automated systems minimize prejudice and variations in analysis, we developed an automated, quantitative coronary analysis system utilizing an IBM PC-XT computer. Film images (35 mm) were cine-to-video converted and subsequently digitized by an IBM PC-XT computer. Given an approximate center line, the computer automatically detected edges, corrected for X-ray magnification, and calculated arterial dimensions. On objects of known dimensional sizes, the correlation coefficient between actual and calculated dimensions was 0.996 (p less than 0.01) with a standard error of estimate of 0.07 mm and +/- 3.0% reproducibility. For objects less than 1 mm in diameter, the standard error of estimate was 0.05 mm with +/- 4.1% reproducibility. However, with minimal contrast material (25%), the standard error of estimate increased to 0.20 mm with +/- 7.2% reproducibility. The results indicate that automated, quantitative coronary angiography can be achieved using an inexpensive IBM PC-XT based system, provided that the vessels are adequately opacified.