Microbiological investigations were carried out on 524 intrauterine pessaries (IUP) from 488 patients. All patients underwent a gynecological examination on the occasion of IUP extraction. An actinomycete colonization of the extracted IUPs could be detected by culture in 8% of the cases. Actinomyces israelii was cultured most frequently. The raised detection of anaerobic bacteria in the endocervix of patients with actinomycin detection constitutes a potential danger for these women with regard to the development of genital actinomycosis. In addition, the clinical parameters document a higher susceptibility of these patients to ascending genital infections. The infectious morbidity is significantly raised.