An experimental study was carried out to evaluate the protective role of an endoluminal prosthesis on high risk colo-colonic anastomoses. One hundred and fifty rats were divided into two groups: Group E with endoluminal latex prosthesis and Group C without. Bursting pressure and collagen concentration in the perianastomotic tissue were tested, respectively, on the 4th, 7th and 12th, and 4th, 7th, 12th, 18th and 38th postoperative days. Bursting pressure was significantly higher in Group E on the 4th postoperative day. There was no significant difference in the anastomotic collagen concentration between the two groups. The presence of the prosthesis did not produce any macroscopic or microscopic evidence of impaired healing or stricture at the suture line. Death due to anastomotic dehiscence occurred in 11/75 (15%) in Group C and in 1/75 (1.3%) in Group E (p less than 0.01). Endoluminal prosthesis appears to have a protective effect on anastomotic healing. The mechanism is probably due to mechanical protection and not to differences in collegen concentration.