In a preliminary study of the transmission rate of Ureaplasma urealyticum, Mycoplasma species, Gardnerella vaginalis, B-Streptococci, Candida species and Chlamydia trachomatis from the mother to the newborn, swabs were taken from 45 parturients and their neonates and cultured by suitable methods. Out of 30 parturients with a positive culture, 8 harboured more than one microorganism investigated. U. urealyticum was found in 11 newborn and all of them had a positive mother. Candida spp. were found in 4 newborn, but 3 of these had a negative mother. G. vaginalis was detected in only 1 infant and the mother was negative. C. trachomatis was not isolated from any mother but was present in 2 newborn infants. Thus only U. urealyticum showed clear evidence of transmission from mother to baby.