An experimental study in rats was designed to determine the effects of z-plasty on the patency of microvascular anastomosis. Eighty Sprague-Dawley rats of mixed sex were divided into two groups. In all animals, the left carotid arteries were used. In the first group (n=40), a single z-plasty was done at the anterior side of the carotid artery before end-to-end anastomosis was performed. In the second group (n=40), end-to-end anastomosis with interrupted sutures was done. Patency and the appearance of the anastomosis were evaluated 1 hr later, on the seventh postoperative day, and at the end of the third postoperative week. There was no vasospasm demonstrated in the first group. Patency rates were 100 percent for both groups after 1 hr. On the seventh postoperative day, one anastomosis in the first group (patency rate, 97.5 percent) and two anastomoses in the second group had failed (patency rate, 95 percent). Patency rates were similar at the third week. The difference was not statistically significant (p=0.5). Histologic examinations demonstrated that z-plasty did not cause any adverse effects at the vessel wall or at the anastomosis.