131 patients aged 25-35 followed from 1969-84 underwent endometrial biopsies under antibiotic cover preliminary to insertion of IUDs. 125 subsequently had IUDs inserted, including 10 Dalkon Shields, 50 Gravigards, and 66 copper 200, Gyne-T, or Nova T devices. All IUDs were inserted in the 1st 10 cycle days under a 3-day antibiotic cover. The 131 biopsies revealed 18 simple endometrial hyperplasias, 1 glandulo- cystic hyperplasia, and 5 endometrial polyps. The hyperplasias were treated with a progestin on cycle days 15-25 for 3-6 months and a curettage was performed for the polyps. No cases of endometritis were found in nulligestes. The 11 patients with latent endometritis were treated with antibiotics for 10 days and were vaccinated with an antipyogenic. A repeat endometrial biopsy was done to confirm disappearance of the endometritis before the IUD was inserted. The 126 IUD users were followed for 6 years on average. 2 cases of salpingitis and an adnexal reaction were observed. 2 of the 3 were treated with antibiotics and had no complications. The 3rd underwent tubal microsurgery after which she became pregnant. The IUD was removed in all 3 cases at the onset of symptoms. 1 of the 3 patients did not have a preliminary endometrial biopsy before the IUD was inserted. Despite the small sample size, it appears that a preliminary endometrial biopsy can reduce the infection rate among IUD users to that of the general female population.