Mycoplasma hominis and Ureaplasma urealyticum can be isolated with considerable frequency from the human urogenital tract and are thought to cause various syndromes such as nongonococcal urethritis, pelvic inflammatory disease, pyelonephritis or infertility. The aim of this study was the evaluation of the presence of different genital pathogens in patients with sexually transmitted diseases (STD) and, in particular, the detection of mycoplasmas in individuals infected with genital microbes and an assessment of the presence of genital microorganisms in patients harbouring Mycoplasma hominis or Ureaplasma urealyticum. Furthermore, the occurrence of mycoplasmas in women with bacterial vaginosis was established. Specimens were collected from a total of 41,980 persons attending the Outpatients' Centre for Infectious Venero-Dermatological Diseases in Vienna from 1994 to 1996. Of all genital pathogens, Ureaplasma urealyticum was cultured most frequently in men and women. Mycoplasma hominis and Ureaplasma urealyticum were detected more often in the vaginal fluid than in the male urethra. By contrast, infection rates with Neisseria gonorrhoeae and Chlamydia trachomatis were higher in men than in women. In both men and women, trichomoniasis increased colonisation with Mycoplasma hominis, while mycoplasmas occurred less frequently together with genital candidiasis. Mycoplasma hominis was cultivated significantly more often in women with bacterial vaginosis than in those without. In contrast to urethral infections in men, cervical infections with Neisseria gonorrhoeae or Chlamydia trachomatis raised the incidence of Mycoplasma hominis in the vaginal fluid.