Although there has been no systematic study of the morphology of collagen and elastin fibers in atherosclerotic plaques, most of the detailed descriptions and many of the published photographs of both human and experimental lesions include information concerning the structure, distribution and relative proportions of these elements. A general qualitative overview and some semi-quantitative statements can therefore be formulated. Precise spatial reconstructions of elastin and collagen distribution in plaques from published data are hampered by two serious limitations. First, the sections have usually been taken from the most complex portions of plaques. The disrupted central portion of an advanced or complicated atheroma may not be the best site for observation of the architectural details which might help to unravel plaque morphogenesis. A second limitation is the usual failure to reproduce the in vivo configuration of arteries and plaques during fixation. Statements concerning the orientation of plaque and artery wall fibers can not be made readily from undistended material.