As a result of reports received by the Food and Drug Administration (FDA) of false-positive results obtained with FDA-cleared in vitro diagnostic kits for the detection of Toxoplasma-specific human immunoglobulin M (IgM) antibodies, an FDA-sponsored evaluation of six kits was performed. A battery of 258 serum specimens, including 30 specimens drawn 1 to 5 months after initial Toxoplasma infection and 228 specimens from Toxoplasma IgG-positive individuals, Toxoplasma IgG-negative individuals, rheumatoid factor-positive persons, and persons determined to be Toxoplasma IgM positive by commercially available assays, was assembled, randomly assorted, and coded. The battery was tested at the FDA with six commercially available kits, at the Palo Alto Medical Foundation (PAMF) by the PAMF double-sandwich IgM enzyme-linked immunosorbent assay (PAMF IgM ELISA), and at the Centers for Disease Control and Prevention (CDC) by the CDC EIA IgM. The results of the PAMF IgM ELISA that were obtained with the battery were considered to be the "gold standard" for this study; specificity rates were computed by considering the PAMF results to be 100% specific. Sensitivity and specificity rates were found to be as follows: CDC EIA IgM, 100 and 99.1%, respectively; Abbott IMx Toxo IgM, version 1, 100 and 77.5%, respectively; Abbott IMx Toxo IgM, version 2, 93.3 and 97.3%, respectively; Abbott Toxo-M EIA, 100 and 84.2%, respectively; BioMérieux Vitek VIDAS Toxo IgM, 100 and 98.6%, respectively; BioWhittaker Toxocap-M, 100 and 95.9%, respectively; Gull Toxo IgM, 97 and 85.6%, respectively; and Sanofi Diagnostics Pasteur Platelia Toxo IgM, 100 and 96.8%, respectively. Although the extent of false-positive reactions with these kits cannot be calculated because the study was retrospective and sample choices were biased, the results may be useful as an indicator of the relative specificities of these kits.