We assessed the utility of culture for Mycoplasma pneumoniae and Chlamydophila pneumoniae to diagnose respiratory tract infections. Compared to PCR and IgM serology, culture was less sensitive and had extremely low yield. Culture is not recommended for these pathogens, and this method should be eliminated from routine practice.The etiology of respiratory tract infections can be difficult to diagnose by health care practitioners because clinical history and symptoms are usually nonspecific for most communityacquired pathogens. Mycoplasma pneumoniae and Chlamydophila pneumoniae cause up to 22% of community-acquired pneumonias and 5 to 10% of cases of tracheobronchitis, pharyngitis, laryngitis, and sinusitis (3-4, 7, 10, 12). Historically, culture has been the gold standard for diagnosis. However, cultivation of these microorganisms can prove challenging because they are fastidious and may require weeks for growth. Serology is more convenient and sensitive than culture, but results are often delayed, and false-negative test results often occur early in the course of illness. Although not standardized, nucleic acid-based tests, such as PCR, provide fast and sensitive results. While such tests are not always available on site in many medical centers, the 24-to 48-h delay in transit time may still be acceptable given the higher diagnostic yield of PCR.Despite the obvious limitations of culture, physicians continue to order this test frequently. In recent years, ARUP Laboratories has received large numbers of requests, including more than 3,000/year for M. pneumoniae and more than 1,500/ year for C. pneumoniae culture. Studies focusing on the value of culture either have been small in scale or have used type strains or patient isolates rather than direct patient specimens (8,13). An accurate and reliable diagnosis of M. pneumoniae and C. pneumoniae is important to differentiate them from other common respiratory pathogens because their treatments differ (1). Being aware of the poor sensitivity of culture for these pathogens, we found the high numbers of test requests for M. pneumoniae and C. pneumoniae culture from respiratory tract specimens to be concerning and to require further investigation. To examine more closely the utility of culture for diagnosing respiratory syndromes, we compared its performance to those of nucleic acid testing and serology for detection of M. pneumoniae and C. pneumoniae.From 2003 to 2008, microbiology results of culture, PCR, and serology performed at ARUP Laboratories for M. pneumoniae and C. pneumoniae were retrospectively reviewed with a specific focus on respiratory specimens (e.g., nasal wash, nasopharyngeal swab, bronchoalveolar lavage, tracheal aspirate, sputum, and pleural fluid) for PCR and culture. Respiratory specimens were transported either refrigerated or frozen, except for C. pneumoniae culture, for which only refrigerated specimens were transported. Additional data were collected for M. pneumoniae culture (1995 to 2003). C. pneumoniae enzyme-linked immunosorbent assay (ELI...