Using dogs, we experimentally produced devascularized areas in the small intestine and colon and took quantitative measurements of the submucosal local blood flow using the hydrogen clearance method.. In the area slightly toward the ischemic side of the devascularized margin, local blood flow is less on the mesenteric side in both the ileum and the colon, and microcirculation is better maintained in the colon that in the ileum. When the anastomosis was performed in the area in which the local blood flow on the mesenteric side was 60 per cent of the control value in the ileum or 70 per cent in the colon, recovery of the control value was achieved by the seventh postoperative day. When anastomosis was performed in the area in which the local blood flow on the mesenteric side was 15 per cent of the control value in the ileum and 22 per cent of the control value in the colon, the flow on the mesenteric side did not recover to the level of the control value by the seventh postoperative day, and anastomotic leakage occurred in some dogs. All anastomotic leakage occurred on the mesenteric side. The local blood flow rate at the point at which the last signal was detected by Doppler ultrasound flowmeter after moving Doppler probe from the devascularized margin toward the ischemic side was 57 per cent of the control value in the ileum and 54 per cent of that in the colon. Such levels of blood flow are considered sufficient for successful healing of tissue after an anastomosis.