Of 474 women studied to identify epidemiological and clinical correlates of chlamydial infection of the cervix, Chlamydia trachomatis was isolated from 158 (33.3%) of all women, from 48.3% of those infected with Neisseria gonorrhoeae, from 43% of the sexual consorts of men with nongonococcal urethritis, and from 74% of those whose consorts were also infected with C trachomatis. C trachomatis was the sole pathogen found in 58 women. Age, marital state, occupation, past history of gonorrhoea, menstrual state, and symptoms had no predictive value. The isolation of C trachomatis was significantly associated with N gonorrhoeae, the use of oral contraceptives, cervical ectopy, cervicitis, and last sexual exposure more than one week previously. Except for three patients, none of the criteria alone or in combination was reliable enough to predict with acceptable accuracy that the 30 chlamydia-positive women among the 191 who were not infected with N gonorrhoeae and whose consorts were not known to have urethritis harboured chlamydia.