I evaluated performance of the Mycoplasma pneumoniae-specific IgM antibody rapid detection test (ImmunoCard Mycoplasma, IC, Meridian, USA) and compared it to the particle agglutination (PA) test and ELISA tests (Mycoplasma pneumoniae IgG, IgA, IgM ELISA medac, Medac Diagnostika, Germany). Serum samples numbering 112 were obtained from 70 pediatric patients (<16 years old) with M.pneumoniae infection diagnosed by a PA test (four-fold or greater rise by paired serum samples or >/=1:640 by a single serum sample). Of these, 82 samples (73.2%) were positive in IC and 91 (81.3%) positive in ELISA IgM tests. Specifically, for samples obtained within 7 days following the onset of fever, 6 of the 14 positive in the ELISA IgM test were negative in IC and 4 of the 18 samples negative in the ELISA IgM test were positive in IC. I ascribed this difference to the difference in antigens used in each test. In the analysis of sequential serum samples from 2 patients with M.pneumoniae pneumonia, IC was still positive in 248-and 527-day samples for which a PA test and the ELISA IgM and IgG tests indicated no acute infection. Nine (36.0%) of 25 serum samples obtained from apparently healthy adult volunteers were positive in IC. Of the 9 IC-positive cases, ELISA tests suggested possible recent infection at most in 3 cases, while the remaining 6 cases had no evidence of acute infection. In conclusion, although IC is sufficiently sensitive as a rapid screening test for detecting M.pneumoniae-specific IgM antibody, a positive result in the test does not always indicate acute infection by this organism. To ensure accurate diagnosis of M. pneumoniae infection, paired serum samples are thus required for conventional methodologies.