PIP: Spermicidal contraceptives, after falling out of favor in the 1960s, are once again being sought be women desiring a natural and safe method. 2-6% of couples in France and other European countries are estimated to use spermicidal contraceptive methods. There is a wide an puzzling gap between the theoretical efficacy of spermicides tested in vitro and efficacy in actual practice. The theoretical failure rate of spermicides used regularly and correctly is 0-7.6%. The principal spermicides used in France at present are the ionic surfactant agent benzalkonium chloride and the nonionic surfactant nonoxynol 9, which destroy the cellular membranes of the sperm. Several tests are used to determine the spermicidal activity of a contraceptive. They include the International Planned Parenthood Federation test which is considered positive if 1 ml of a 1/11 solution immobilizes the sperm in .2 ml solution of selected sperm within 10 seconds in a reproducible fashion; the study of the minimal concentration that completely inhibits .2 ml of fresh sperm in less than 20 seconds; the absence of penetration of sperm in hamster eggs after contact with the products tested, and the Huhner test consisting of a search for sperm in the cervical mucus in the hours following intercourse. The 4 tests have demonstrated that the spermicidal efficacy of benzalkonium chloride is 4 times greater than that of nonoxynol 9. The spermicidal action is reinforced by thickening and coagulation of the mucus on contact with benzalkonium chloride, and the action of the spermicide covering the vaginal mucus. The practical efficacy of spermicides, which takes into account failures attributable to the method itself as well as failures due to incorrect use, is reflected in Pearl indexes ranging from 0.3-30. The efficacy of spermicides is closely related to their correct use. The method should be used regularly and systematically and the product inserted before initiation of sexual contact. Most products require renewed application if intercourse is repeated. Package instructions about duration of action and waiting times for the product to become fully effective should be carefully followed. The product should be left in place at least 2 hours. Baths and vaginal douches should be avoided for 4 hours after intercourse. Products such as soaps which neutralize the ionic surfactants should be avoided. Spermicidal contraceptives are recommended only for women capable of understanding and following the use instructions. Women who find the idea of spermicides distasteful and those requiring absolute efficacy should select another method. Vaginal spermicides may be suggested for women over 40 and those with contraindications to oral contraceptives and IUDs. They provide some protection against sexually transmitted diseases, and have no effects on the vaginal mucus or menstrual cycle and no carcinogenic effect.