The efficacy of elemental diets and antibiotics in colon preparation was evaluated in 90 rats. Controls were unprepared. Five treatment groups received, in addition to magnesium sulfate catharsis, elemental diets: Vivonex, Flexical, clear liquids only, clear liquids and pre- and postoperative parenteral antibiotics (cephalothin sodium and kanamycin sulfate, intramuscularly), and clear liquids and orally administered antibiotics (neomycin sulfate and lincomycin hydrochloride) for four days. Partial colectomy and colon anastomosis were done in each animal. Observation of weight loss preoperatively and seven days postoperatively, survival, mean tensile anastomotic strength, weight gain, and the incidence of anastomotic leak and wound infection led to the following conclusions: Elemental diets were as effective as orally administered antibiotics in decreasing the incidence of postoperative infection. Elemental diets or antibiotics were not superior to mechanical preparation alone. Elemental diets did not prevent anastomotic leak or enhance anastomotic mean tensile strength. Mechanical bowel emptying using clear liquids and cathartics remains the key to short-term preoperative colon preparation.