A suture mesh of polyglactin 910 [Vicryl (polyglactin 910) suture mesh] was placed as a patch graft into the thoracic aorta of 23 growing pigs. In three other pigs the mesh was grafted in the form of a tube to replace a short aortic defect. The biological processes taking place in the grafted area were studied by morphological methods. The following observations were made: (1) Hemostasis readily occurred by fibrin, platelet, and erythrocyte embedding of the mesh. (2) Early outgrowth of smooth muscle cells around the mesh took place from the normal aortic media and from a newly formed subintimal smooth muscle layer. (3) The newly formed arterial tissue was completely endothelialized within 20 days. (4) The polyglactin mesh had disappeared almost completely at 40 days, but the new wall seemed to retain sufficient strength throughout the observation time. (5) Only irregular deposition of elastic fibrils occurred, but in other respects the new tissue structurally resembled normal arterial tissue.