The study covered 110 pregnant females during the period from January 1, 2002 till April 30, 2003. Nine females (8.18%) delivered premature newborns. Samples were taken from the posterior vaginal fornix and canalis cervicalis in the 18th and 24th gestational week. The preparations stained after Gram were examined under light microscope. Microbial cultures on blood agar were examined, too. It was established that 18 or 16.36% of all the cases presented with cultures positive for group B streptococci (Str. agalactiae) and Ureaplasma urealythicum. Some other microbial flora representatives such as Chlamydia trachomatis, Neisseria gonorrhoea and Trichomonas vaginalis were additionally identified. The independent colonization with Str. agalactiae prior to the 18th gestational week does not relate to the spontaneous abortions and premature deliveries at all. On the other hand, the colonization with Group B streptococci or their symbiosis with other microorganisms after the 23rd-24th gestational week displays a certain correlation with the premature births.