We tested in vitro the activities of streptomycin and tetracycline-antibiotics that have long been used to treat rhinoscleroma-as well as several newer oral agents by using 23 isolates of the causative organism KlebsieUla rhinosckeromatis. All isolates were inhibited by clinically achievable concentrations of trimethoprim-sulfamethoxazole, amoxicillin-clavulanate, chloramphenicol, ciprofloxacin, cephalexin, cefuroxime, and cefpodoxime.Klebsiella rhinoscleromatis causes rhinoscleroma, a chronic granulomatous infection of the upper airways. This disease occurs sporadically in the United States (3,11,19); but it is endemic in parts of Europe, Africa, Central and South America, and southern Asia, where thousands of humans may be afflicted (12). Prolonged antimicrobial treatment is required to cure rhinoscleroma. Streptomycin in combination with tetracycline has long been regarded as the standard treatment (7, 10), although rifampin (7, 8) has more recently been found to be effective either by topical application or oral ingestion. Trimethoprim-sulfamethoxazole (TMP-SMX) (1, 7) has also been recommended, but this recommendation has been made in the absence of published clinical trials. Anecdotal reports describe the efficacy of expanded-spectrum cephalosporins (3). No systematic in vitro study of the antibiotic susceptibility of K rhinoscleromatis has been described for two decades, and the efficacies of more recently available antibiotics that are administered orally have not been reported. We examined the in vitro inhibitory and bactericidal activities of antimicrobial agents that have traditionally been used to treat rhinoscleroma as well as those of some newly available ones. Since prolonged treatment is required in treating this disease, we directed our study toward orally available antimicrobial agents.Twenty