The in vitro susceptibilities of 98 isolates of JK diphtheroids to teichomycin, vancomycin, and eight other antibiotics was investigated. Teichomycin and vancomycin were extremely active against all the isolates tested. The 90% minimal inhibitory concentrations for teichomycin and vancomycin were 1.56 and 0.78 micrograms/ml, respectively. The majority of the isolates were resistant to ticarcillin, methicillin, erythromycin, tetracycline, chloramphenicol, clindamycin, and cephalothin.