In a randomized study 100 patients, 78 males and 22 females, with uncomplicated gonorrhoea were treated with either a single oral dose of 250 mg of ciprofloxacin or a single oral dose of 3 g of amoxycillin and 1 g of probenecid. Three of the gonococcal strains produced penicillinase and, in addition, nine strains had MIC-values of amoxycillin ranging between 0.6 and 1.2 mg/l and five other strains MIC-values higher than 1.2 mg/l. Twenty-two patients had a concomitant infection due to Chlamydia trachomatis. All patients treated with ciprofloxacin were cured, while two patients treated with amoxycillin had treatment failures. Neither treatment regimen had any effect on the chlamydial infections. No adverse effects were observed. It was concluded that ciprofloxacin is the drug of choice in the treatment of uncomplicated infections due to Neisseria gonorrhoeae.