Inadequate blood flow causing tissue hypoxia can result in failure of anastomotic healing. Tissue oxygen tension (ptO2) measurement has been used to predict anastomotic leakage in animals, but its use in humans has not been described previously. A Clark-type oxygen electrode was used to measure ptO2 on the colon of 50 patients undergoing colonic resection and anastomosis. Baseline ptO2 levels were lowest on the descending colon (31.8 +/- 7.4 mmHg, mean +/- SD) and tended to increase at all sites with increasing arterial paO2 (r greater than .76, P less than .001). Perianastomotic ptO2 levels were predictive of subsequent anastomotic leakage when they were less than either 20 mmHg; 50 percent of the preresection ptO2; 15 percent of the arterial paO2; or 40 percent of the ptO2 at a control site (ileum). It is concluded that perioperative ptO2 measurements are of value in the prediction of anastomotic leakage.