The existence of normal lower reproductive tract flora has been recognized for many years. A study was conducted to identify the possible existence of upper reproductive tract (endometrial) bacteria in asymptomatic women with no history of previous pelvic infection and a normal pelvic examination. Bacteria were recovered from the endometria of 55 women with a double-lumen-catheter-protected brush; six cultures were sterile. Two hundred thirty-one bacterial species were present in 54 endocervical cultures. Type of contraception and phase of the menstrual cycle had no significant effect on the bacterial species recovered. Although contamination by cervical bacteria was possible, there was evidence of separate endometrial flora.