Fleroxacin (Ro 23-6240) is a new trifluorinated quinolone exhibiting high activity against a broad spectrum of gram-negative and gram-positive bacteria. Fleroxacin is characterized pharmacokinetically by a long elimination half-life (9 to 10 h) and high concentrations in plasma (e.g., maximum concentration of 2.3 micrograms/ml after an oral dose of 200 mg). Fleroxacin (Ro 23-6240) is effective against Haemophilus ducreyi in vitro. Fleroxacin (Ro 23-6240), 200 or 400 mg as a single oral dose, is efficacious therapy for microbiologically proven chancroid in patients who do not have concurrent HIV-1 infection. Among HIV-1-infected men, a single dose of 200 or 400 mg of fleroxacin is inadequate therapy for chancroid.