In a randomized comparative study, 83 male patients suffering from acute uncomplicated gonococcal urethritis were treated with a single dose of either 0.8 g pefloxacin, given orally, or 1.0 g cefotaxime, given intramuscularly. The cure rates were 100% in both treatment groups four to seven days and 21 to 31 days, respectively, after therapy. The MICs of the isolated Neisseria gonorrhoeae ranged from 0.008 to 0.06 mg/l for pefloxacin and from 0.0005 to 0.03 mg/l for cefotaxime. Postgonococcal urethritis was found in 9% of the patients treated with pefloxacin and in 20% of the patients treated with cefotaxime. Chlamydia trachomatis, Mycoplasma hominis and Ureaplasma urealyticum were isolated from 15%, 7% and 22% of the patients, respectively, before therapy and from 22%, 11% and 20% of the patients, respectively, 21 to 31 days after therapy. Both antibiotics had no effect on the presence of these microorganisms. No side effects were recorded in either groups of patients except that 46% of the patients treated with cefotaxime reported mild pain at the injection site. In conclusion, pefloxacin and cefotaxime are safe and effective agents in the treatment of uncomplicated gonococcal urethritis in men.