1,265 patients having elective surgery with colectomy for cancer or sigmoiditis have been included in four successive randomized multidepartmental studies in order to define the most effective preparation, reducing the rate of postoperative infections, and the shortest one. The first study included 202 patients divided up into 2 groups, and compared a three-day conventional preparation (CP) (low-residue diet, laxatives and enemas) with a total digestive irrigation (TDI) (9 liters in 6 h) with Mannitol. Both preparations were associated with a three-day preoperative antibiotic therapy with Neomycin and Tetracyclin. Intolerance to TDI (50% of cases) and the greater number of fistulae with this method lead to preferring CP. The second study (326 patients in 4 groups) compared on one hand, a CP with the single absorption of a sachet of Sennosides or 2 liters of 10% Mannitol, and on the other hand, the preoperative antibiotic treatment utilizing Neomycin or Tetracyclin over three days with a 24-hour treatment with Metronidazole. Its conclusions are that the absorption of Sennosides is better tolerated than Mannitol and significantly more effective than the CP. There is no significant difference between the antibiotic therapy over three days and that over 24 h. The third study (335 patients in 4 groups) compared on one hand, lukewarm water enemas to enemas with iodinated polyvidone diluted to 5%, and on the other hand an antibiotic therapy utilizing Metronidazole on the day before, the same day and the three following surgery with a 24-hour antibiotic therapy utilizing Metronidazole (1.5 g) and/or Cefotaxime (4 g) on the same day as the operation.(ABSTRACT TRUNCATED AT 250 WORDS)