The purpose of this study was to assess the prevalence of resistance to aminopenicillins and metronidazole among selected subgingival species in dental patients from Yemen and Norway. Three subgingival samples were collected by paper points from each of 34 Yemeni and 21 Norwegian adult volunteers and then pooled. Each of the 55 pooled samples was plated on fastidious anaerobic blood agar containing 2 microg/mL ampicillin or metronidazole, or no antimicrobial. Species identification of growth was done using DNA-DNA checkerboard hybridisation. The overall proportion of ampicillin resistance among the 18 identified species was 28.9% and 7.9% in the Yemeni and Norwegian samples, respectively, whereas for metronidazole it was 60.3% and 11.3%. The number of species resistant to ampicillin and metronidazole was significantly higher (P