In this study we tried to determine the factual prevalence of Chlamydia trachomatis seropositive women. Sera of 174 sexually active women of reproductive age who attended the emergency room in our gynecology department were tested by both a species-specific solid-phase enzyme immunoassay (SPEIA, ImmunoComb, Orgenics, Israel) and by an immunoperoxidase assay (IPA). One-hundred and twenty-two of 174 women (70.1%) tested were found positive for C trachomatis by the IPA test. The SPEIA test identified 41 (33.6%) of those as positive for C. trachomatis and 81 (66.4%) positive for C. pneumoniae. We conclude that the currently used IPA method for chlamydia diagnosis overestimates C. trachomatis infection and its specificity for the diagnosis of C. trachomatis is limited. By using the SPEIA test, it is possible to distinguish between C. trachomatis and C. pneumoniae seropositivity.