Intraluminal pressure adjacent to left colonic anastomoses. A cumulative total of 89 h of pressure data was acquired from both sides of a left colonic anastomosis in 15 patients over a median period of 7 postoperative study days. Patients had a colonic ileus lasting 3-10 days and during this proximal and distal inactivity the intraluminal pressure remained within 6 mmHg of atmospheric pressure. After recovery of activity, pressures proximal to the anastomosis in excess of 10 mmHg occurred during less than 1 per cent of the recording time. Distal peak pressures were significantly elevated with respect to the proximal site (P less than 0.001). Two-thirds of the distal pressures recorded were between 10 and 20 mmHg and 98 per cent were less than 50 mmHg; the peak distal pressure was 90 mmHg. Four patients had distal repetitive tonic contractions creating a pressure difference across the anastomosis with a mean of 20 mmHg and a peak of 45 mmHg. Each contraction persisted for 15-20 min. Intraluminal pressures are unlikely to play a role in anastomotic dehiscence. 