The frequency of isolation of Chlamydia trachomatis from the cervix of patients with acute salpingitis has varied between 5% and 40%. A significant change in the titer of antibodies to C. trachomatis, as studied by microimmunofluorescence tests, has been found in 18% to 46% of patients with acute salpingitis. In salpingitis patients in whom C. trachomatis is isolated from the cervix, such a change in titer has been found in 31% to 54%. Patients with Chlamydia-associated salpingitis are generally young and do not appear severely ill. The erythrocyte sedimentation rate is generally higher in such patients than in women with salpingitis not associated with chlamydial infection, and the inflammatory reaction in the fallopian tubes is more severe than would normally be expected from the relatively benign clinical picture. The only reliable means of diagnosing chlamydial salpingitis is by laparoscopy. In chlamydial salpingitis, all layers of the tubal wall usually show an inflammatory infiltration. The mucosa is destroyed either totally or patchily. Experimental infections in grivet monkeys have fulfilled Koch's postulates. Evidence is accumulating that post-chlamydial salpingitis is a major factor in tubal infertility.