Norfloxacin, an orally administered quinoline carboxylic acid that is structurally related to nalidixic acid, has been shown to be highly active in vitro against penicillinase-producing Neisseria gonorrhoeae. Ninety-two men with culture-proved gonococcal urethritis, 46 per cent with penicillinase-producing N. gonorrhoeae, and 27 per cent with non-penicillinase-producing N. gonorrhoeae that was resistant to penicillin were given either 1200 mg of norfloxacin divided into two equal oral doses four hours apart (59 patients) or 2 g of spectinomycin intramuscularly (33 patients). All patients in both treatment groups were cured. No adverse reactions were reported in either group. We conclude that a two-dose, single-day regimen of orally administered norfloxacin is effective therapy for uncomplicated urethritis caused by penicillin-resistant strains of N. gonorrhoeae.