The cervical bacterial flora of 18 healthy, parous, sexually active women was analysed before, and 3-5 months after insertion of a copper-releasing intrauterine device (IUD) and after long-term use of an IUD for 3-5.5 years in another nine women. No significant differences were found in the number of aerobic bacteria isolated before or after IUD insertion or after long-term use of an IUD. In contrast to aerobic bacteria, significantly more anaerobes were isolated in the cervix of women having used an IUD for several years when compared to those using barrier contraception with a condom. None of the women had clinical signs of pelvic infection and a cervical bacterial flora rich in anaerobes can be regarded as a normal finding in healthy sexually active women using an IUD for contraception.