A controlled trial of one- and two-layer inverting techniques of sutures for the contruction of high and low colorectal anastomoses was conducted on 137 patients, the integrity of the suture lines being assessed clinically and by routine radiological examination after a small Gastrografin enema. A clinical diagnosis of anastomotic leakage was made in 9 patients (or perhaps more accurately in 5 only), but subclinical dehiscence was demonstrated radiologically in a further 39 patients (or perhaps 43). There was a slightly greater incidence of dehiscence after the one-layer technique of suture for both high and low anterior resection.