In this experimental study the effect of peroperative faecal soiling on immediate postoperative anastomotic leakage after resection and primary anastomosis of a left colon obstruction was evaluated. Faecal soiling was quantified by a standardized irrigation of the abdominal cavity and then culturing of the fluid. An increased peroperative soiling was found after resection of a stenosis compared to resection of a non-stenotic bowel. Anastomotic complications were correlated to the degree of bacterial contamination and a breakpoint of 10(4) CFU/ml was found. Immediate postoperative leakage, tested with the bacteria Serratia marcescens, was not increased in the stenosis group. Thus, peroperative bacterial contamination seems to be one important factor in developing anastomotic complications after resection of colonic obstruction while an immediate leakage of bacteria through the anastomosis seems to be less important.