One hundred eighty left colonic single-layer end-on anastomoses performed on 90 rats by microsurgical techniques, using polydioxanone monofilament absorbable sutures, were examined histopathologically and microangiographically at nine different times, from two to 180 days. There was no anastomotic leakage. The vascular state after suturing and the evolution of the neovascularization are described. The neovascularization appeared to follow the same process of evolution as tissue restoration. It began early, was greatest on the seventh day, and diminished thereafter. When granulation tissue was narrow, the anastomoses were barely hypervascular, the neovascularization assured by submucosal plexus. A voluminous granulation tissue was hypervascular, had a slower evolution, and neovascularization was then assured above all by the peritoneal formations adherent to the suture.