A half-strength povidone-iodine (Betadine) solution was used topically as part of the preoperative chemical preparation of the eye. Aerobic and anaerobic bacterial cultures of the conjunctiva were taken before and after the chemical preparation in 30 consecutive patients; the second eye served as a control. In the control eyes, no significant change in the number of colonies or species of bacteria was found. In the povidone-iodine-treated eyes, the numbers of colonies decreased 91% and the number of species decreased 50% (statistically significant). We therefore recommend that a half-strength povidone-iodine solution be used as part of the chemical preparation of the eye for surgery.