Eleven patients were colonized or infected with diphtheroids identified as Corynebacterium xerosis. All the patients were compromised hosts by nature of their underlying disease and/or therapy. Two patients developed bacteremia following colonization of the respiratory tract with C. xerosis. Other patients were colonized at various sites, which included the respiratory tract, abdominal and thoracic wounds, amputated limb, and arterial-venous shunt. Distinctive features for the identification of C. xerosis include negative reactions for hemolysis, urease, and motility, and positive reactions for catalase, glucose, sucrose and nitrate reduction. Antimicrobial susceptibility tests were performed by the disk diffusion method. In many instances the organisms were resistant to the antimicrobial regimens received by the patients. This was most frequent for nafcillin, gentamicin, kanamycin, clindamycin, and chloramphenicol. On the other hand, the organisms were highly susceptible to penicillin, ampicillin, cephalothin and carbenicillin.