In order to explore the respective role of wound healing and suture material on metachronous carcinogenesis at colonic lines in rats, tumour yield was studied after the administration of a chemical carcinogen (azoxymethane) at the moment that in one group of rats most of the suture material was still present and crypt cell proliferation elevated, while in another group, no more suture material was present and crypt cell proliferation rate (CCPR) normalized at the anastomotic site. Azoxymethane (15 mg/kg/week, s.c, during 6 weeks) was administered in male Sprague-Dawley rats (n = 105) 8 weeks after the creation of an anastomosis in the ascending and descending colon with either stainless steel sutures (group A, n = 30) or fast-absorption Vicryl (Vicryl Rapide®, group B, n = 30). A control group (group C, n = 30) underwent a sham laparotomy before the administration of azoxymethane, while the animals of a fourth group (group D, n = 15) were not operated upon and received no azoxymethane. Twenty-six weeks after the first injection of azoxymethane there was no significant difference in the total colo-rectal tumour yield in the three operated groups (A, B, C), but a significantly greater proportion of anastomotic tumours (28/68 vs. 13/88, p < 0.01)and more anastomotic tumours per rat (28/23 vs. 13/28, p = 0.01) as well as more rats with anastomotic tumours (16/23 vs. 11/28, p = 0.04) were found in the steel-sutured group (A), compared with the control group (C). No significant differences were observed in tumour distribution between the groups in which the anastomoses were carried out with Vicryl Rapide (B) and the control group (C). Thirty-six weeks after operation steel sutures were recovered in 30.4% (7/23) of the left-sided anastomoses and in only 8.7% (2/23) of the right-sided anastomoses. At that time, CCPR was significantly elevated in the left-sided anastomoses only, while the CCPR in the right-sided anastomoses was normal when compared with all the other groups (A, B, C and D). The present study showed a shift in the distribution of tumours towards the anastomotic sites at which suture material was present and the CCPR raised, at the moment of carcinogen administration, confirming the importance of the interaction of sutures with the mucosa in tumour formation. The actual elimination process of the suture material might influence the CCPR and act as a cocarcinogenic factor. In view of these observations, either the use of strictly inert suture material or the development of sutureless anastomotic techniques should be encouraged in the construction of colonic anastomoses