To determine the effect of douching on the quantitative and qualitative makeup of the vaginal microflora.We first evaluated the effect of douching with a solution of physiologic saline to determine the effect of washing the vaginal surface. Two douche preparations, one containing 0.04% acetic acid and one containing 0.30% povidone-iodine, were evaluated subsequently to determine whether any effects occurred in addition to those noted with saline. Duplicate vaginal swab samples were obtained at predetermined intervals from ten healthy volunteers for three sampling cycles before and after use of the douche preparations for various periods of time. Samples were analyzed for total facultative and obligately anaerobic bacterial populations.The use of a douche preparation containing acetic acid caused a transient reduction of the total bacterial counts, with most of the change attributable to the effect of washing the surface of the vaginal vault as noted with physiologic saline. In contrast, the povidone-iodine preparation caused a significant reduction in total counts compared with those obtained after use of a physiologic saline solution by the same subjects (P = .02). Little change in the qualitative makeup of the vaginal microflora occurred.The use of povidone-iodine douches decreases the numbers of the dominant bacterial species beyond those expected with other douches. In some individuals, such changes may allow rapid proliferation of potential pathogens during this altered state, increasing the risk of associated infections.