We compared the performance of Testpack Chlamydia to tissue culture isolation for detection of endocervical chlamydia in an obstetric clinic population at high risk for infection. Among 227 evaluable patients, 30 tissue culture-confirmed chlamydial infections were found (13.2%). The sensitivity, specificity, and positive and negative predictive values of Testpack compared with tissue culture isolation were 66.7, 95.4, 69.0, and 94.9%, respectively. This test can be performed on a desktop within 30 minutes by staff with limited laboratory experience and no special equipment. Based upon our preliminary experience, we believe that Testpack Chlamydia offers promise as a screening device for the detection of endocervical chlamydial infections in highrisk obstetric populations.