The bacterial colonizing of the intrauterine device (IUD) and its tail were studied in 152 IUDs obtained from 70 symptomless IUD wearers, 13 women with dysfunctional bleeding, 23 women with pelvic inflammatory disease, 31 women in whom the tail of an IUD was no longer visible and 17 women who were pregnant with an IUD in situ. The IUDs were either removed by the transcervical route or through a fundal incision in the uterus after hysterectomy. Most IUD were heavily contaminated by bacteria, especially Staphylococcus epidermidis, Enterococci and anaerobic Lactobacilli. The number of colonies was higher in women with dysfunctional bleeding and pelvic inflammatory disease than in others with a predominance of pathogenic bacteria, namely beta-hemolytic Streptococci, Staphylococcus aureus and Escherichia coli. Almost half of the IUDs without a tail protruding through the cervix were sterile. With pregnancy in the presence of an IUD, 71% of devices grew bacteria which were mainly anaerobic.