From 1983 to 1986 more than 2000 non-pènicillinase producing Neisseria gonorrhoeae from Amsterdam, The Hague and Rotterdam were auxotyped and screened for susceptibility to 10 antibiotics by MIC determination. By far the commonest auxotypes were N.R. (non-requiring; 40%) and Pro− (proline requiring; 30%). During that period there was a substantial shift in the ratio of both auxotypes-roughly from 1:2 to 2:1—in The Hague. Pro− isolates were generally less susceptible than N.R. isolates, and there was a strong positive correlation between the MICs of the different drugs. The prevalence of isolates with a penicillin MIC equal to or above 0·5 IU/ml amounted to 14%, while in only 1% was the MIC above 1 IU/ml. Comparing our results with an earlier study by Stolz, Zwarte & Michel (1975, British Journal of Venereal Diseases 51, 257–64), the level of resistance to penicillin among non-PPNG has not significantly increased in The Netherlands since 1972. The prevalence of isolates showing relative resistance towards tetracycline and thiamphenicol (MIC 2–4 mg/l) decreased from approximately 20% in 1983/84 to approximately 10% in 1985/86, coinciding with a drop in the prevalence of Pro− isolates. All strains were susceptible to cefuroxime and spectinomycin and highly susceptible to cefotaxime and riprofloxacin.