Leakage and stenosis are serious complications of gastrointestinal anastomotic surgery that may, in part, be related to local ischemia. The ability to accurately quantitate the degree of gastrointestinal anastomotic ischemia remains a challenging clinical problem. The purpose of this study was to: 1) develop a model of colorectal anastomotic stenosis following local ischemia; 2) compare the accuracy of laser Doppler velocimetry and intramural colonic pH in quantitating critical levels of intestinal anastomotic ischemia; and 3) compare the anastomotic healing process using either a standard two-layer Czerny-Lembert handsewn or EEA™ stapled anastomotic technique under ischemic conditions. The studies reported here were performed in two phases. Phase I was the pilot study in which the authors developed a model of colorectal anastomotic ischemia and defined critical levels of ischemia using laser Doppler velocimetry and intramural pH (≤200 mV; ≤7.0, respectively). These parameters were then tested prospectively in Phase II, assessing the effects of anastomotic ischemia on animals kept alive for 5, 11, 21, and 60 days after surgery. Overall there was a 70 percent incidence of anastomotic healing complications in the Phase II trial with laser Doppler velocimetry correctly predicting anastomotic outcome in 70 percent of cases and tissue pH in 93 percent of cases. The results indicate that, although laser Doppler velocimetry and intramural pH measurements provide safe, easy techniques for assessing the effects of ischemia on the colorectal anastomosis, measurement of intramural pH provides an optimal quantitative method for predicting subsequent anastomotic outcome and tissue viability. © 1990 American Society of Colon and Rectal Surgeons.