&NA;This study explores the role of sutures and the healing colonic wound in experimental carcinogenesis. One hundred sixty rats underwent surgery with colotomy and repair using silk, steel, or Vicryl®(Ethicon, Somerville, NJ) sutures or a sutureless technique. Forty rats had a sham procedure. All animals received azoxymethane for 12 weeks at a dose of 10 mg/kg/week. Half the rats commenced carcinogen before surgery, and half commenced it eight weeks after surgery. Animals with anastomotic tumors were found in 46 percent of the sham group(P<0.05cf.sutured), 41 percent of the sutureless group(P<0.02cf.sutured), and 68 percent of the sutured group. The corresponding figures for anastomotic carcinoma were 9 percent(P<0.001cf.sutured), 22 percent, and 38 percent. No significant differences in tumor yield were noted among the different sutures. However, several differences were noted between the two carcinogen models. In those animals that received surgery first, there was a higher incidence of anastomotic tumors(P<0.002) and cancers(P<0.0001) in the sutured and sutureless groups, and those tumors that occurred in the sutured group were considerably larger than in those that had carcinogen first (15.9 mmcf.4.9 mm;P<0.0001). Overall, all sutures seem to enhance anastomotic tumor formation, and we would suggest that a sutureless anastomosis may diminish this risk.