Two hundred and fifty-four specimens from males and females consulting a clinic for sexually transmitted diseases were analyzed for genital Chlamydia trachomatis infection. Each clinical sample was tested by the cell culture technique and the polymerase chain reaction using a closed system. When the two test systems were compared, the overall sensitivity of the polymerase chain reaction was 96% and the specificity 94% when compared to the cell culture technique. By use of a closed system for DNA extraction and sample transfer for the polymerase chain reaction, contamination of the samples was minimized. The polymerase chain reaction detected a higher number of Chlamydia trachomatis infections among both symptomatic and asymptomatic females and males, and it also detected Chlamydia trachomatis at an earlier stage of infection when compared to cell culture. The polymerase chain reaction did not detect Chlamydia trachomatis after sufficient antibiotic treatment of the chlamydial infections.