The MIC of gemifloxacin and five other quinolones was tested against 31 clinical isolates of Neisseria gonorrhoeae; strains were analyzed for the presence of mutations in both the gyrA and parC genes. Only seven strains were resistant to nalidixic acid due to a mutation in the gyrA gene but not in the parC gene, with six and two considered intermediate to ciprofloxacin and levofloxacin, respectively. The activity of gemifloxacin was similar to that of trovafloxacin and moxifloxacin, but was more active than nalidixic acid, ciprofloxacin or levofloxacin against the gyrA mutant strains. Gemifloxacin is a valid therapeutic alternative to treat infections with N. gonorrhoeae, retaining its activity against strains already presenting a mutation in gyrA. © 2003 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved.