Cervical smears from 1,784 women who attended the family planning clinics of the Institute for Research in Reproduction were examined for the presence of Actinomyces-like organisms. Among 815 intrauterine contraceptive device (IUD) users, the repeat smears from 57 women were positive for Actinomyces-like organisms, giving a prevalence rate of 6.99%. Immunofluorescent staining using specific antisera confirmed the presence of A. israelii in all 57 women. Forty IUD users whose smears were positive for Actinomyces-like organisms underwent bacteriologic culture studies; A. israelii was isolated in 23 of these cases. The clinical findings at the time of smear collection in the 57 IUD users were within normal limits. The initial cervical smears of all IUD users and both the initial and repeat smears of all nonusers were negative for Actinomyces-like organisms. The data indicate that prolonged use (greater than 2 years) of an inert or copper intrauterine device promotes the overgrowth of Actinomyces in the vagina and that this can be detected by routine cervical cytology.