The objective of this study is to compare the effectiveness and safety of pefloxacin to ofloxacin in the treatment of gonococcal urethritis. Ninety-five male patients with uncomplicated gonococcal urethritis from the STD clinics at Ramathibodi Hospital, Mahidol University  and Vachira V.D. Clinic, Department of Communicable Diseases Control, Ministry of Public Health were enrolled. They were randomly allocated to treatment regimes of either 400 mg pefloxacin or 400 mg ofloxacin as a single oral dose. Clinical, bacteriological and safety assessments were made at entry, and 3 or 7 days after treatment. Neisseria gonorrhoeae was eradicated in 95 percent (37/39), and 97 percent (31/32) of patients treated with pefloxacin and ofloxacin, respectively. Overall 24 percent (20 in 82) of the isolates produced penicillinase (PPNG isolates). The MIC range of both drugs was the same, between 0.03-2.0 mg/l. The MIC 90 of ofloxacin was 0.25 mg/l but it was 1 mg/l for pefloxacin. We concluded that 400 mg of pefloxacin was as effective as 400 mg of ofloxacin in the treatment of male gonococcal urethritis.