The clinical usefulness of polymerase chain reaction (PCR) for the diagnosis of trichomoniasis was evaluated in comparison with other conventional tests. PCR was used for specific detection of Trichomonas vaginalis by primers based on the repetitive sequence cloned from T. vaginalis (TV-E650). Between June 1996 and August 1997, 426 patients visited the department of obstetrics and gynecology, Hanyang University Kuri Hospital and were examined for trichomoniasis using wet mount examination, Papanicolaou (Pap) smear, culture and PCR. One hundred and seventy-seven patients (group A) visited with the symptoms of vaginal discharge and 249 patients (group B) visited for regular cervical Pap smear with no vaginal symptoms. From group A (n = 177), 3 infections (2.0%) were detected by wet mount, 6 infections (3.3%) by Pap smear and culture, and 17 infections (10.4%) by PCR. From group B (n = 249), 4 patients (1.6%) were found to have T. vaginalis by culture and 6 infections (2.4%) were detected by PCR. Therefore, in both groups, PCR for T. vaginalis showed a higher detection rate compared with conventional wet mount, Pap smear or culture. The detection by PCR was specific for T. vaginalis since no amplification was detected with DNAs from other protozoa and Candida albicans. The sensitivity and specificity of PCR were 100%. This method could detect T. vaginalis in vaginal discharge at a concentration as low as 1 cell per PCR mixture. These results indicate that PCR could be used as a specific and sensitive diagnostic tool for human trichomoniasis.