The breaking strength of anastomoses in the left colon in the early phase of healing was studied in rats fed low residue diet (Biosorbin MCT) and the results were compared to those from rats fed standard laboratory diet. Further, eventual correlation between mechanical strength development and collagen content in the colonic wall around the anastomosis was evaluated. The anastomotic strength with sutures in place decreased by approximately 30% of the immediate postoperative value during the first two days in both groups of animals. There was no correlation between changes in anastomotic strength and collagen content at that time. After the second day there was a gradual increase of anastomotic strength, reaching the strength at day 0 after 7 days. The regain of strength was mainly due to collagen deposition in the anastomosis. Despite more collagen deposition in animals on standard laboratory diet the anastomoses had comparable strength development in the two groups. It was concluded that low residue diet does not impair the suture holding capacity or the anastomotic strength. Instead there was some evidence for a more uncomplicated healing when the bowel content was diminished.