Ultraviolet light-inactivated elementary bodies of Chlamydia trachomatis serovar E were fluorescently tagged with rhodamine isothiocyanate (5 micrograms/ml) and added to primary cultures of human endometrial gland epithelial cells. The elementary bodies, at a multiplicity of infection of 600:1, were allowed to adsorb to the cell monolayers for 1 hour at 35 degrees C in an atmosphere of 5% carbon dioxide. The monolayers were disaggregated by trypsinization and the individual cells were processed in the fluorescent activated cell sorter for chlamydial attachment. This method of analysis revealed attachment of C. trachomatis to approximately 50% of human endometrial gland epithelial cells. Addition of estrogen (10(-10) mol/L) to the culture medium enhanced chlamydial attachment to human endometrial gland epithelial cells to approximately 80% (p less than or equal to 0.005), and progesterone in combination with estrogen reduced chlamydial attachment in a dose-dependent fashion: 1 ng/ml progesterone, approximately 50%; 5 ng/ml, about 30%; 10 ng/ml, about 18%, respectively (p less than or equal to 0.025).