Cervical swabs and in many cases also intrauterine contraceptive devices were examined from 973 women for the presence of Actinomyces israelii. It was detected in 11.6% of these women, the majority of whom were asymptomatic. The detection, however, of A. israelii in the female genital tract was associated with an almost 4-fold increase in the incidence of pelvic inflammatory disease (PID), indicating that colonization may progress to an infection in a small number of women. The incidence of A. israelii in the female genital tract of IUCD wearers was more than doubled when the IUCD was worn for longer than 4 years. The type of IUCD worn did not appear to be an important risk factor. Immunofluorescent staining of cervical smears identified 64% of cases. Specific culturing for A. israelii or cytological screening of Papanicolaou smears in addition were required to increase the isolation rate to nearly 90%.