Probiotics are defined as live micro-organisms which, when administered in an adequate amount, confer a health benefit on the host. Probiotics have been shown to displace and kill pathogens and modulate the immune response by interfering with the inflammatory cascade that leads to preterm labour and delivery. Lactobacilli are the dominant bacteria of vaginal flora and possess antimicrobial properties that regulate other urogenital microbiota. Incomplete cure and recurrence of genitourinary infections lead to a shift of the local flora from a predominance of lactobacilli to coliform uropathogens. Use of Lactobacillus-containing probiotics to restore commensal vaginal flora has been proposed for the treatment and prophylaxis of bacterial urogenital infections. The actual mechanism of action of probiotics in the vagina is probably multifactorial. The production of lactic acid, bacteriocin, and hydrogen peroxide seems to be important, and modulation of immunity is another possible mechanism. The administration of these Lactobacilli by mouth or intravaginally, or both has been shown to be safe and effective in reducing, or treating, or both, urogenital infections. For pregnant women, such restoration could be important to prevent BV and lower the risk of PTL Daily use of oral gelatin capsules containing dried viable Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 has been shown to decreased e risk of bacterial vaginosis and maintain normal lactobacilli vaginal flora. These organisms are antagonistic to the growth and adhesion of various intestinal and urogenital pathogens including Salmonella typhimurium, Shigella sonnei, E coli 0157, toxic shock Staphylococcus aureus, group B streptococci, Enterococcus faecalis, G vaginalis, and uropathogenic E coli. In animal studies, these strains were found to be safe during pregnancy and to enhance the health of mothers and newborns. Studies are under way in Toronto, Ont, to test the effects of these strains on bacterial vaginosis in pregnant women at risk of preterm labour. These lactobacilli might also have a role in preventing vaginal colonization by group B streptococci, organisms that can cause serious illness and even death in newborns. Certain lactobacilli can inhibit growth and adhesion of streptococci in vitro, but whether they can do this in vivo is untested.