A new method has been developed for the quantitative assessment of atherosclerotic lesions, in which a conventional xerox machine is the sole equipment used. As an example, the aorta from a cholesterol-fed rabbit was removed in toto, opened longitudinally along its anterior margin, flattened in a transparent polypropylene bag and then xeroxed. The outlines of the atherosclerotic lesions were traced on translucent graph paper ruled into 1 mm squares. The squares within those outlines were counted and expressed as a percentage of the whole surface. This xerographic method is rapid and reproducible and is achieved without changing the magnification; it gives comparable or better results than other staining methods. As the aortic specimen is undamaged by fixation or staining, the specimen can be used for subsequent morphological or biochemical studies. Thus, the degree of surface involvement can be correlated with other morphological or biochemical changes in the same arterial samples.