For identification of those variables in the history and in the clinical and routine laboratory examination that are most likely to indicate infection of the uterine cervix with Chlamydia trachomatis, 284 women attending a venereal disease clinic were studied, of whom 58 (20.4%) yielded the organism from the cervix. Women with chlamydial cervical infection showed no distinctive symptoms. Although associations were found between the presence of C. trachomatis and cervical discontinuity, purulent cervical exudate, and inflammatory changes in cervical cytology, these signs were not pathognomonic of chlamydial infection since they were also seen in some women infected with other microorganisms. There was a significant relationship between the presence of antibodies, detected by immunofluorescence, and the recovery of C. trachomatis in cell culture. There were no associations between ethnic group, history of sexually transmitted disease, method of contraception, phase in the menstrual cycle, or numbers of sexual contacts and infection with C. trachomatis.