Preoperative and postoperative cultures of the upper vagina were taken from 48 women who underwent vaginal hysterectomy. They received a five-day course of either prophylactic cephalosporins or placebo. Comparisons of preoperative and postoperative flora in both the active-drug and placebo groups as well as comparisons between the postoperative flora of the drug group and that of the placebo group were made. Alterations of the bacterial flora occurred whether or not the patient received prophylactic antibiotics.