IgM anti-P1-reactive strips were produced as previously described, and the assay was performed as previously reported. The utility of this test has previously been described in detail. The Immunocard Mycoplasma IgM was performed under the conditions recommended by the manufacturer. Among 54 control sera from asymptomatic adults, there were 4 positive reactions (4/54; 7.4%) by Immunocard Mycoplasma IgM. One of these was a strong positive color change, and three were positive but weaker than the control test port color reaction. For the 49 sera from symptomatic patients for whom a diagnostic test was requested, IgM anti-P1 immunoblotting was reactive for 19 (38.8%). The sensitivity, specifi city, positive predictive value, and negative predictive value for Immunocard Mycoplasma in comparison to IgM anti-P1 immunoblotting was 73.7% (14/19), 90.0% (27/30), 82.4% (14/17), and 84.4% (27/32), respectively. Accordingly, an error rate for the commercial test of 16.3% (8/49) would have occurred. Among 30 sera which were negative by IgM anti-P1 immunoblotting, 3 (10.0%) were positive by the commercial assay; this is similar in frequency to the 7.4% frequency among adult control sera. All the latter 3 positive assays were weaker in color reaction than the control port. For the sera which were IgM-reactive by the IgM anti-P1 immunoblotting only, 4 were strongly reactive and 1 was of intermediate reactivity. The applicability of the rapid IgM assay will most certainly depend on the prevalence of infection. When the prevalence is high, such as among the sera of this study, such a diagnostic test will appear more favorable. The prevalence of M. pneumoniae among etiological agents of respiratory infection will certainly be variable, and will be infl uenced by the prominence of various viral etiological agents, especially in the winter season. The positive test frequency of 7%–10% among uninfected patients is consistent with the fi ndings for other similar diagnostic tests. This is likely in large part to be attributed to the commonality of M. pneumoniae respiratory infection in the community. The frequency of IgM reactivity with IgM anti-P1 immunoblotting, however, is considerably less. Received: September 30, 2007 / Accepted: October 31, 2007