First catch urine (FCU) from 751 asymptomatic adolescent female high school students, with sexual debut, were screened for the presence of Chlamydia trachomatis (Group A). The prevalence of C. trachomatis infection in Group A was 2.1% (16/751). In Group B, 619 asymptomatic adolescent females attending a youth and a family planning clinic were screened for C. trachomatis by testing FCU and cervical specimens. An enzyme immunoassay (IDEIA-III) was used to detect C. trachomatis verified by fluorescein isothiocyanate-conjugated (FITC) monoclonal antibodies. Only samples positive in both tests were regarded as true positive. The cervical samples from the women in Group B were positive in 7.8% (48/619), while the FCU were positive in 6.0% (37/619). Detection of C. trachomatis by EIA in FCU samples was found useful for screening females for genital chlamydial infection. The prevalence of C. trachomatis in an unselected asymptomatic population was found to be lower than in age-matched individuals seeking medical advice in the same coherent area.