An investigation of chlamydial infection in sexual contacts of patients with nongonococcal urethritis (NGU) was carried out to determine the clinical signs of infection in the cervix, and their response to chemotherapy, and the incidence of cervical infection in the presence of ectopy and oral contraception. In 202 consecutive female contacts of NGU the isolation rate of Chlamydia trachomatis was 35%. Hypertrophic ectopy and endocervical mucopus were present in 19% and 37% of chlamydia-positive patients respectively and, in all but one, resolved after treatment. Only 14% of those followed up after treatment developed yeast infections. The chlamydial isolation rate was significantly higher in patients with hypertrophic ectopy and endocervical mucopus. Cervical ectopy and oral contraceptives acted additively, each producing a significant effect on the chlamydial isolation rate in the presence of the other but not when present alone.