Cylinders of soft polyvinyl soaked in benzalkonium chloride have been used as contraceptive tampons. Benzalkonium chloride is a powerful spermicide which belongs to the cationic or saponium detergents. It does not enter the blood stream. These contraceptive sponges are more efficient and better accepted by patients than spermicides used by themselves. One of the principal advantages of the method is to be able to place the tampon in position hours before sexual intercourse. The authors wanted to test if wearing a tampon for a long time did not have an adverse effect on the cervico-vaginal epithelium. 27 women were seen before and after having worn one of these contraceptive tampons for 24 hours: neither the smears nor colposcopy had changed. 21 vaginal biopsies were taken after the tampon had been removed from the area where it had been lying. Vaginal epithelium tolerates the prolonged presence of the sponge well. The authors carried out bacteriological controls before and immediately after removing the tampon 24 hours later. Commensals were still present. Pathogenic sexually transmitted organisms are moderately sensitive to bactericidal action of benzalkonium chloride except for candida albicans, which is resistant. There was no increase in the number of germs in 69 cases studied. The authors carried out scanning electromicroscopy at different magnifications to see the effect on normal cervical mucus at the time of ovulation when it came into contact with benzalkonium chloride. Ovulatory mucus which had been translucent and fluid became thicker and coagulated and the reticulated web took on the appearance of a bunched up web.(ABSTRACT TRUNCATED AT 250 WORDS)