A total of 409 serum and cerebrospinal fluid specimens from human subjects with proven coccidioidomycosis, with other infections, or with no apparent illness were tested for antibodies to Coccidioides immitis by the Premier EIA (Meridian Diagnostics, Inc., Cincinnati, Ohio), which tests for immunoglobulin G (IgG) and IgM responses to coccidioidal antigens, and by the conventional complement fixation (CF) or immunodiffusion (ID) assays for antibodies corresponding to those detected by the tube precipitin (TP) or CF tests. Of the 409 specimens, 47 were from persons with confirmed coccidioidomycosis and all were positive for C. immitis antibodies in IDCF tests and enzyme immunoassays (EIAs) for both IgG and IgM. The EIA for detecting both IgG and IgM antibodies proved to be sensitive for detecting coccidioidomycosis case sera positive by the IDCF, IDTP, and CF tests. Maximal sensitivity for diagnosing coccidioidomycosis is dependent upon detection of both IgG and IgM antibodies in the EIA. The EIA, however, was not absolutely specific, since some sera from patients with confirmed blastomycosis and some from patients with noncoccidioidal disease produced false-positive reactions.