The objective of this study was to evaluate the usefulness of a Papanicolaou stained urethral smear (Pap smear) to identify sexually transmitted disease (STD) pathogens in men with urethritis. Specimens from the endourethra were obtained for Chlamydia trachomatis and Neisseria gonorrhoeae cultures, a Gram stain, and a Pap smear in 24 symptomatic men aged 16-22 years. All Pap smears were read independent of the culture results. Based on the laboratory techniques employed, nine subjects had gonococcal urethritis (GU), and 11 had nongonococcal urethritis (NGU). Four subjects with GU had concomitant infection with another STD pathogen(s). Papanicolaou smear alone identified four different pathogens in 16 subjects, chlamydia in ten, trichomonads in two, intracellular diplococci in two, multinucleate giant cells of herpes in one, and chlamydia and trichomonad together in one. Out of 11 chlamydia-positive Pap smears, three had a positive culture. One subject had a positive chlamydia culture and a negative Pap smear. Two subjects with intracellular diplococci on Pap smear had culture-confirmed gonorrhea. The Pap smear was useful in identifying some of the different pathogens in NGU, especially trichomonads and herpes, not recoverable by commonly used techniques and in the diagnosis of concomitant infection by more than one STD pathogen in GU. Adding the Pap smear to the diagnostic tests for urethritis increased the etiologic diagnoses from 37.5% to 79%.