Bacterial colonization and infection of wounds in seriously burned patients often comes from the patient's indigenous bowel flora. A prospective randomized clinical trial that involved 30 patients with 20% or greater total body surface area burns was undertaken to evaluate the use of a standard antibiotic bowel preparation in the delay or prevention of bacterial colonization of the burn wound and sepsis. Certain enteric bacteria were seen less frequently in the treated group (Enterobacterorganisms), but other bacteria appeared more often in the treated group (Proteusorganisms and enterococci). The average time of colonization of the burn wounds was 6.1 days in the treated group and 6.7 days in the control group. Blood cultures were positive for enteric organisms earlier in the treatment group. Pseudomonads appeared earlier in the wound and blood cultures of the treated group than in the control group. The effect of antibiotic bowel suppression in patients with burns is varied and unpredictable. The bowel preparation may select certain organisms and lead to earlier colonization of the wounds. Overall outcome and survival was not improved by the use of an antibiotic bowel preparation in these patients.