Antibody detection is the most versatile and commonly used method for measles diagnosis. Detection of specific IgM antibodies in a single serum specimen collected within the appropriate time after rash onset can provide a good presumptive diagnosis of current or recent measles infection and is the test of choice for rapid diagnosis of measles cases. So, optimal timing for collection of a single serum specimen to diagnose measles by IgM capture Enzyme Immunoassay (EIA) was evaluated. 399-paired sera were tested for measles IgM antibody. 149-paired sera were measles IgM negative. Two hundred fifty paired sera had at least one IgM positive. 223-paired sera were positive in both first and second samples. 19-paired sample were negative in first and positive in second sample and 8-paired sera were positive in the first and negative in the second samples. 85% and 100% of first specimens within 7 and 7-21 and 94% of all second samples were IgM positive at 28th days after rash onset, respectively. Analysis of data indicates that a single serum specimen collected between 7 to 27 days after rash onset can be used to diagnose most cases of measles with an IgM capture EIA.