The diagnosis of N. gonorrhoeae infections depends upon the demonstration of the bacterium, and this is commonly done by cultivation. The laboratory diagnosis of N. gonorrhoeae was greatly facilitated by the introduction of the Thayer-Martin selective medium containing vancomycin, colistin and nystatin in its present formula (Thayer and Martin, 1966). An alternative combination of antimicrobial drugs in the selective medium, consisting of lincomycin and colistin, was proposed by Berger (1966) and Potuznik and Hausner (1969). In the bacteriological laboratory of the City of Goteborg, Sweden, about 150,000 specimens are processed each year for the cultivation of N. gonorrhoeae. This laboratory uses a modification of the Thayer-Martin medium without the addition of nystatin. Vancomycin, included in the Thayer-Martin combination of antibiotics, has been shown to inhibit the growth of certain gonococcal strains (Reyn, 1969; Cross, Hoger, Neibaur, Pasternack, and Brady, 1971). This initiated a study to investigate how common these strains were in Goteborg, and its environs, and whether they could be isolated on another medium suitable for routine use. Material and methods In October and November, 1972, a preliminary study was performed on 254 samples from 145 selected patients. The samples were cultivated both on the standard plate containing colistin and vancomycin and on the same plate without antibiotics. Samples were taken with charcoal-treated swabs and transported in a modified Stuart's medium. The plates were inoculated, the inhibitory plate first, and incubated for 40 hrs at 36°C.; gonococci were identified by their colonial and microscopic appearance, oxidase reaction, and fermentation tests. Later, a second study was performed on 1,418 samples from 609 non-selected patients. In this study urethral, cervical, and rectal swabs were obtained from the female
