Trichomonas is a cause of nongonococcal urethritis (NGU); however, studies of its prevalence in men have been hampered by the lack of sensitive diagnostics. DNA amplification allows for reappraisal of the extent of infection in men. Men attending a sexually transmitted diseases clinic were tested for trichomonas, chlamydia, and gonorrhea. The prevalence of these pathogens was 17%, 19.6%, and 17.7% respectively. In men with NGU, 19.9% were infected with trichomonas. These data have implications for treatment of NGU and control of trichomoniasis.