&NA;To evaluate the effects of povidone‐iodine (PI) enema on the bacterial flora of colorectal mucosa, the authors studied 113 patients who were candidates for colorectal surgery. The study of the rectum included 72 patients. Total bacterial concentrations after a PI enema (N=44) were significantly lower than after a simple water enema (N=12,P<0.001), or than after a water enema associated with intravenous metronidazole (N=16,P<0.01). The study of the colon included 41 patients. Total bacterial concentrations did not differ after a PI enema (N=24) than after a water enema (N=11); both groups were associated with intravenous metronidazole. In contrast, both preparations significantly reduced bacterial concentrations when compared with oral administration of polyethyleneglycol (N=6,P<0.01). Similar results were observed in rectal and colonic studies, when analysis was restricted to the anaerobic flora. PI is an antiseptic that, when administered alone in an enema or in association with metronidazole, significantly reduces bacterial concentrations in the mucosa of the colon and rectum. It may be proposed as a simple preoperative preparation for colorectal surgery.