Objective: To investigate the carcinogenic role of suture materials in an experimental model in rats., Design: Laboratory, experimental study., Setting: University hospital, Spain., Subjects: 125 Sprague-Dawley rats in 5 groups of 25 each., Interventions: 3 Different suture materials (silk, polydioxanone, and titanium staples) were implanted in a region of the colon in 75 rats divided into three groups of 25. Another 25 animals were injured by puncture only in the same region, and a further 25 rats were not operated on (controls). Injections of 1-2,dimethylhydrazine were then given for 26 weeks., Main Outcome Measures: Number of rats in each group who had tumours in the region of interest, and level of infiltration of the tumours in each group., Results: There were no differences between the injured and control rats in the number of tumours in the study zone. All groups in which suture material had been inserted had tumours in this zone. Titanium was more carcinogenic than either silk or polydioxanone. The tumours associated with titanium were the most infiltrating., Conclusions: We recommend the use of absorbable sutures, with a careful follow-up of patients in whom titanium staples have been used.