The prevalence of Chlamydia infection in 95 sex partners was determined by both polymerase chain reaction (PCR) and cell culture. Thirty-three (18%) of 186 specimens were positive by culture and 61 (33%) were positive by PCR-EIA. PCR was positive in 75% (21/28) of male partners of PCR-positive women compared with culture, which was positive in only 45% (9/19) of male partners of culture-positive women (P =.053). For female partners of infected men, the difference was less marked. PCR was positive in 58% (21/36) of female partners of infected men versus culture, which was positive in 56% (15/36) offemale partners of culture-positive men. The correlation of PCR between partners and sequence analysis of Chlamydia DNA showing the same sequence from sex partners of 7 couples support the accuracy of the assay. These data suggest that PCR is more sensitive than culture for detection of Chlamydia trachomatis, particularly for male partners of infected women. © 1993 by The University of Chicago.