Case report. To illustrate the usefulness of broad-range bacterial polymerase-chain-reaction (PCR) testing in osteoarticular infections by Capnocytophaga canimorsus. C. canimorsus is a gram-negative bacillus that was first identified in 1976. It is a normal inhabitant of the oral mucosa of dogs (26%) and cats (15%). The main clinical patterns are septicemia, which may cause fatal septic shock (in 30% of cases) but arthritis and discitis are possible. C. canimorsus is susceptible to many antimicrobials including β-lactam antibiotics. About a case report of 54-year-old man transferred to our institution for discitis, we discuss about PCR for C. canimorsus discitis diagnosis. At admission, the only abnormal physical finding was global pain and stiffness of the lumbar spine. Radiographs of the lumbar spine and pelvis showed lumbar spondylosis, degenerative disc disease, and previously known degenerative facet joint disease. Magnetic resonance imaging indicated L3-L4 discitis with damage to both vertebrae and adjacent discs. Findings were negative from blood and urine cultures, serological tests for the HIV and brucellosis, and sputum tests for Mycobacterium tuberculosis. A percutaneous biopsy of the L3-L4 disc was performed but the bacteriological studies recovered no organisms. A second needle biopsy was performed for broad-range 16S rDNA PCR testing, which identified C. canimorsus. Broad-range PCR provided the microbiological diagnosis of culture-negative discitis in our patient. Broad-range PCR should be considered in patients with culture-negative osteoarticular infections.