&NA;Whole‐gut irrigation was compared with conventional mechanical bowel preparation in a prospective, randomized study. All 100 patients had a combination of ampicillin and metronidazole during and after colorectal surgery. Patients' complaints were equally frequent during the two preparations and were severe in 15 per cent. Gastric position of the tube for irrigation resulted in severe complaints in 3 of 26 patients and in the duodenal position, in severe complaints in five of 24. The time for irrigation was shorter than that for conventional preparation.Deep wound infections were equally frequent after irrigation (3/46) and conventional preparation (4/47). Seven patients were excluded, since no bowel resection had been performed. Collapse of the small and large intestine, as evaluated blindly during surgery, was more frequent after irrigation (P<0.05). Anastomotic leaks after left side resections were less frequent in patients with collapse of the small (P<0.001) and large (P<0.05) intestine.Five leakages among 29 patients after conventional preparation in contrast to one among 22 after whole‐gut irrigation favor the latter, even if this difference did not reach statistical significance (0.05<P<0.10), since anastomotic leakage is lethal in a high number of patients.