Editor: Rothia dentocariosa is an aerobic or facultatively anaerobic, non spore forming, nonmotile, pleomorphic gram-positive rod. Although it is an inhabitant of the human oropharynx, R. dentocariosa has been mostly isolated from patients with endocarditis, arteriovenous fistulas, and pneumonia as an opportunistic pathogen (1). In this report we described the second known case of R. dentocariosa peritonitis in a continuous ambulatory peritoneal dialysis (CAPD) patient, the first being reported by Bibashi et al. in 1999 (2). A 50-year-old man with end-stage renal disease came to the emergency room with abdominal pain and mild fever. He began hemodialysis in 1993 and has now been on CAPD since 1998. Dialysate effluent was cloudy and WBC count was 2000/mm3. Predominance of neutrophils was observed on Gram stain but there were no micro-organisms identified. Two peritoneal dialysate samples (10 mL) were injected into Bactec 9210 (Becton Dickinson, MD, U.S.A.) blood culture bottles. Bacterial growth was determined on the second day via detection of CO2 production. Rough colonies were observed in subculture. On Gram stain, branched diphtheroid-like gram-positive cocco-bacilli were observed. These bacteria were tested by API Coryne strips (bioMerieux, Marcy l’Etoile, France). The result code (7050125) was not included in the routine API database. Differentiation of R. dentocariosa from CDC group 3, group A-3, group 5, and Actinomyces viscosus was performed by lysine and ornithine decarboxylation (3). Motility test was negative. It was sensitive to penicillin G, cefazolin, cephalothin, ceftazidime, ampicillin/sulbactam, gentamicin, netilmicin, tobramycin, amikacin, ciprofloxacin, and vancomycin by disk-diffusion method. Because the patient was started on treatment with cefazolin and netilmicin, broth microdilution susceptibility was performed for these two antimicrobials and was determined to be 0.125 μg/mL and 0.25 μg/mL, respectively. Intraperitoneal cefazolin (250 mg per bag four times daily) plus netilmicin (50 mg once per day into the night bag) therapy was continued. During treatment, nasopharyngeal and dental area cultures showed R. dentocariosa. Peritoneal and systemic symptoms improved on the second day of therapy and the patient was discharged on the fifth day after admission. In previous reports (1,4), it has been mentioned that R. dentocariosa might be a peritoneal pathogen. In the first report, the patient was discharged with cure after successful antibiotic treatment and removal of the peritoneal catheter (2). As a member of the group of oral cavity organisms, R. dentocariosa may be a potential pathogen, especially in immunosuppressed patients, in the presence of a prosthetic device such as a Tenckhoff catheter (1,5). In conclusion, although Rothia dentocariosa is not a life-threatening micro-organism, coryneform bacteria isolated from the dialysate of patients with peritonitis may be viewed as the suspect etiologic agent. These displaced contaminants may be the cause of therapeutic failure.