A monoclonal antibody specific forChlamydia trachomatis(Syva Microtrak) was used to stain directly 249, 127, and 67 specimens obtained from the cervix, and the female and the male urethra, respectively. The Microtrak system identified 100% or 23 culture-positive cases from the cervix (prevalence 9.2), 100% or seven culture-positive cases from the female urethra (prevalence 5.5%), and 93% or 14 culture-positive cases from the male urethra (prevalence 22.4%). Because the Microtrak system is readily available, relatively inexpensive, and easy to read with a fluorescent microscope, it should become a valuable tool to assess objectively both men and women suspect for this common sexually transmitted disease.