A prospective study was carried out to compare the effectiveness of 4 commonly employed methods of bowel preparation before colorectal surgery: mechanical, mechanical with an antibiotic against aerobes (neomycin), mechanical with another antibiotic against anaerobes (metronidazole), and finally mechanical with a combination of neomycin and metronidazole. The use of mechanical preparation as the sole method was discontinued halfway through the study for ethical reasons. 53 bowel preparations were carried out on 31 patients, 7 adults and 24 children with mainly Hirschsprung’s disease and imperforate anus. The incidence of postoperative infections ranged from 40 to 46% in the first 3 groups, in contrast to only 6% in the fourth group (p < 0.05). The majority of the organisms isolated were gram-negative bacteria. The results show that a combination of mechanical bowel washout with oral neomycin and metronidazole is a most effective method of bowel preparation before colorectal surgery.