Streptococcus agalactiae (group B streptococcus) is ine of the main causes of serious infection, such as sepsis, meningitis, and pneumonia in newborn babies, as well as an etiological agent in diabetic adults or chronic patiens. It is now universally accepted that in most cases the transmission from a carrier mother to the fetus occurs in the uretus through ascending transmission right before or during delivery. The identification of maternal colonization during the last weels of pregnency is extremely important, as the administration of preventive treatment upon delivery, thus the fetus protection from a possible infection, will depend on such identification. The guildlines developed bu the US Centers for Diseases Control provide indications for optimal treatment of samples to be analyzed for suspected GBS. Specifically, for the detecion of anal-genital carrier status in pregnant woman, sample should be taken on the 35th to 37th pregnancy week, with a vaginal swab and a second anal-rectal swab.