Gonococcal urethritis being highly contagious, the ideal treatment should be effective, well tolerated and relatively cheap. Among antibiotics fulfilling these conditions, thiamphenicol and spectinomycin are widely used throughout the world and particularly in France. However, the ever increasing incidence of infections caused by penicillinase-producing Neisseria gonorrhoeae (PPNG) strains, the growing number of strains with low sensitivity to penicillin and/or other antibiotics and the recent emergence of strains that are highly resistant to penicillin make it necessary from time to time to re-evaluate the main therapeutic approaches to gonococcal urethritis. In this study thiamphenicol and spectinomycin were compared for effectiveness as single-dose treatments of uncomplicated gonococcal urethritis in 207 male patients who consulted at the Clinical and Biological Centre for Sexually Transmitted Diseases, Saint-Louis Hospital, Paris, during April and May, 1985. Prior to the trial the patients had not received antibiotics for at least 2 weeks. They were allocated at random to two therapeutic groups: 89 patients received a single 2.5 g dose of thiamphenicol orally, and 84 patients received a single 2 g dose of spectinomycin by intramuscular injection. In every case the gonococcal origin of the urethritis had been confirmed by culture. The patients were examined 3 to 7 days after treatment for clinical and bacteriological evaluation. Specimens were cultivated on agar-blood medium, and N. gonorrhoeae was also identified by biochemical and antigenic reactions. The minimum inhibitory concentrations (MIC) of the two antibiotics were determined by the agar plate dilution method, using an agar nutrient medium. The possible production of beta-lactamase and the auxotypic and plasmidic profiles of the PPNG strains were investigated.(ABSTRACT TRUNCATED AT 250 WORDS)