Sensitivities of peptostreptococci, streptococci, Actinomyces, bacteroid, and fusobacterial strains pathogenic for the periodontium to wide-spectrum penicillines, cephalosporines, lincomycin, macrolides, metronidasole, and nitasole are compared. New macrolide antibiotics rulide. Macropene, gramicidin C, levomycetin, and rifampicin are highly effective. Some narrow-spectrum drugs, e.g. augmentin, cephalexin, and vancomycin (towards actinomycetes) were highly effective, too.