The effectiveness of a single oral dose of ciprofloxacin in eradicating urethral gonorrhoea was assessed in 18 men who received 250 mg and 26 men who were given 100 mg. All patients, including two infected with beta lactamase (penicillinase) producing strains of Neisseria gonorrhoeae (PPNG), were cured. The drug had no effect on infection with Chlamydia trachomatis or on the incidence of post gonococcal urethritis. Ciprofloxacin may be useful in patients hypersensitive to penicillins and cephalosporins, and the drug may also be useful in urethral gonorrhoea caused by PPNG strains.