Histologic and bacteriologic analyses of endometrium were performed before and on day 15 after minocycline treatment of 20 patients with acute salpingitis. Endometritis was diagnosed in 15 patients before and in nine after treatment. Neisseria gonorrhoeae was recovered from the cervix and endometrium of seven patients but was not isolated after treatment. Chlamydia trachomatis was recovered from the cervix of eight, and from the endometrium of three patients, two of whom had negative cervical cultures. After treatment C. trachomatis was recovered from the cervix of three patients, although two of them had taken aluminum hydroxide for gastric symptomatology during minocycline treatment. Culture of an endometrial specimen revealed no growth of C. trachomatis. The histologic study revealed plasma cell infiltrates in specimens from patients who had cultures positive for C. trachomatis. The results showed that although endometritis is an important manifestation of acute salpingitis, there is no correlation between severity of endometritis and degree of tubal damage.