In order to show the effectiveness of preoperative antiseptic mouthwash the authors undertook a prospective study in 120 patients who underwent elective surgery under general or local anesthesia. Patients were allocated toone of 4 groups, depending on whether the oral cavity was washed preoperatively with 1% cetrimide, chlorhexidine, povidon-iodine or sterilized normal saline solution (control group). Aerobic and anaerobic bacterial samples were taken from the inferior vestibulum mucosa before surgery, 5 min after the start of the operation and at the end of the procedure. The results show a statistically significant reduction in bacterial counts during procedures in which antiseptics are used to wash the oral cavity preoperatively. 1% cetrimide solution was the most successful in reducing intra-oral bacterial counts and produced the longest lasting antiseptic effect. Chlorhexidine is a good option for procedures longer than 1 hour, while povidon-iodine is recommended for procedures lasting up to 1 hour. Normal saline reduced bacterial counts in the specimen taken 5 min after washing but this short-lasting effect is due to mechanical cleansing rather than the antiseptic effect.