An in-house polymerase chain reaction (PCR) test using ribosomal RNA gene primers was compared with chlamydia antigen detection (DIF) and culture for the detection of Chlamydia trachomatis. Five hundred and forty-eight fresh (unstored) genital swabs and 174 urines (collected at the same time) from patients attending a sexually-transmitted diseases clinic were examined. PCR, DIF and culture detected chlamydia in 43, 35 and 42 swabs respectively from the 43 resolved positive cases. The specificity on the resolved negative specimens was 100% for each of the tests. From the urines, PCR and DIF detected the organism in 16 and 15 cases respectively of the 23 resolved positive males tested but in only 2 and 3 cases respectively of the 9 resolved positive females tested. Specificities were 100% in all cases. Both of the non-culture tests manifested problems with urine due to inhibitory activity (in PCR test) or excessive debris (in DIF test) in about 5% of the specimens. Culture of the urines yielded sensitivities of 40% in the males and 22% in the females. Overall PCR was more sensitive than either culture or DIF on both urethral and cervical swabs and urines. The urines yielded less than three-quarters the number of positives that was obtained from the swabs and were considered to be an unsatisfactory specimen for chlamydial diagnosis. It is concluded that PCR is a satisfactory alternative to culture on genital swabs and may be preferable in situations where the viability of the organisms is in question. DIF remains useful because of its speed and simplicity but is insufficiently sensitive to be relied upon by itself.