The present report describes microbial, serological, and histological findings in chlamydial endometritis. Irregular bleeding, frequently seen in salpingitis patients, suggests endometritis, being a common manifestation of that disease. Chlamydia trachomatis is known to be a principal etiological agent of acute salpingitis. Chlamydiae can be recovered from the uterine cavity of such patients. A dense plasma-cell infiltration is seen in patients in whose endometrial epithelial cells chlamydial inclusions are found. A significant antibody response may be demonstrated in such patients. In acute salpingitis, the presence of chlamydial endometritis supports evidence from experimental animal studies that indicate a canalicular spread of chlamydiae from the cervix to the fallopian tubes.