The highest minimum inhibitory concentrations of ceftriaxone and cefotaxime in 89 analysed Neisseria gonorrhoeae isolates amounted to 0.008 and 0.031 micrograms/ml, respectively. In a randomized controlled trial the single intramuscular injection of ceftriaxone 250 mg and cefotaxime 500 mg cured bacteriologically 35 out of 35, and 29 out of 30 patients, respectively, with uncomplicated gonorrhoea. Facing the different phenotypes of the isolates grown before and after therapy in the case of the non-cured patient within the cefotaxime treatment group, reinfection rather than failure has to be presumed. Postgonococcal urethritis occurred about as often in both groups, the percentage amounting to 24.2 and 28.6%, respectively. If side effects were noted at all, they were considered minor: 4 patients belonging to the first and 3 belonging to the second treatment group complained temporarily about pain at the injection site. Due to the data presented here, ceftriaxone and cefotaxime appear equally effective and safe when used in the dose generally preferred, irrespective of differences in in vitro activity and pharmacokinetic behaviour.