AIMS--To evaluate the use of a duplex polymerase chain reaction (PCR) assay for the simultaneous detection of Neisseria gonorrhoeae and Chlamydia trachomatis in clinical samples. METHODS--Genital swab specimens were obtained from both China (203 swabs) and Hong Kong (202 swabs). N gonorrhoeae and C trachomatis were detected in each specimen with a number of tests including enzyme immunoassays (IDEIA) and PCR assays using both single and double primer pairs. The primer pair for N gonorrhoeae was derived from the cppB gene on its cryptic plasmid and the PCR product was 390 base pairs long. For C trachomatis, the PCR product was 473 base pairs long, resulting from amplification of a sequence in the common 7.4 kilobase plasmid present in all serovars. For N gonorrhoeae, PCR results were also compared with those obtained by culture and Gram's smear of the discharges. RESULTS--For the 203 specimens collected in China, similar numbers of positive results (177) were obtained by both Gonozyme and duplex PCR for the detection of N gonorrhoeae. No discrepant results were found among the cultured specimens when Gonozyme and duplex PCR were compared. C trachomatis was detected in 47 specimens by duplex PCR, but was detected in only 28 by IDEIA. Of the 202 Hong Kong specimens, 46 were positive for N gonorrhoeae, detected by both Gonozyme and duplex PCR; 34 were positive for C trachomatis, 25 of which were detected by IDEIA and the remainder by duplex PCR. CONCLUSIONS--The duplex PCR assay is a satisfactory diagnostic tool for the simultaneous detection of N gonorrhoeae and C trachomatis in clinical swab samples. Further evaluation is suggested.