The minimum inhibitory concentrations (MICs) of 18 antimicrobial agents against 104 strains of Neisseria gonorrhoeae isolated in the Brussels area between January and October 1976 have been measured. The MICs for penicillin G, ampicillin, amoxycillin, carbenicillin, and cephalexin showed a bimodal distribution. The second modus strains of cephalexin (MIC = 6.25 microgram/ml) were relatively resistant to penicillin G (MIC greater than or equal to 0.08 microgram/ml). About 51% of all strains were relatively resistant to penicillin G, 40.5% to ampicillin (MIC greater than or equal to 0.16 microgram/ml), 46% to amoxycillin, and 47.5% to carbenicillin. For cephalexin and cephaloridine, 25% and 8.5% respectively of all strains were relatively resistant (MIC greater than 3.12 microgram/ml). For cefazolin all MICs fell into a range of 0.097--3.12 microgram/ml. Resistance to tetracycline, doxycycline, minocycline, erythromycin, and spiramycin (MIC greater than or equal to 1 microgram/ml) was found in 9.5%, 7%, 6%, 36.5%, and 71% respectively of all isolates. No strains were resistant to rifampicin. For chloramphenicol and thiamphenicol the MICs ranged from 0.39 to 12.5 microgram/ml and from 0.195 to 3.12 microgram/ml respectively. The results for sulphamethoxazole, trimethoprim, and the combination of sulphamethoxazole and trimethoprim in a 20:1 ratio are given and discussed. The fractional inhibitory concentration (FIC) indices have also been calculated. No beta-lactamase-producing strains were found, and a contingency coefficient C has been determined for all the pairs of antibiotics investigated