Paired serum samples from 93 patients suspected of having measles were assayed for measles virus-specific immunoglobulin M (IgM) antibodies by an enzyme immunoassay (EIA), and the results were compared with results from a complement fixation assay and an EIA for measles virus IgG. By using significant serologic rises as the standard for comparison, the IgM EIA assay had a sensitivity of 85.7%, a specificity of 81.3%, a positive predictive value of 95.7%, and a negative predictive value of 54.2%. This assay can be expected to perform well in outbreak situations.