The concept of direct reconstruction of damaged and diseased arteries is generally accepted. Currently, the most popular materials used for arterial replacement are autogenous veins and crimped tubes of Dacron and Teflon developed by De Bakey and Edwards and Tapp.2-4,8-10,14,15,32Experimental comparisons of several different replacement materials have been reported.* There are not, however, similar comparisons of the readily available materials currently in use in clinics throughout the country. The first portion of this study is a controlled comparison of these materials when used to bypass short segments of the canine femoral artery. Heretofore, comparative hemodynamic studies of arterial replacements have been concerned primarily with pulse transmission,25graft elasticity,24and relative flow rates.27Actual visualization of flow patterns usually has been accomplished by forcing suspended particles through rigid transparent models.11,26-31Refined cineangiographic techniques, however, are available to study in vivo fluid mechanics.1,30The second