The successful demonstration of Epstein-Barr virus immunoglobulin M (EBV IgM) antibody in human sera has been accomplished to date by at least four groups of workers. Many, however, including ourselves, have had difficulty in getting reproducible results with the techniques described. The three-coat technique described by H. Schmitz and M. Scherer (1972) on both fractionated and unfractioned sera was adopted with minor modifications. The Hyland antihuman IgM antiserum used in the second coat was made specific by absorption on Cohn fraction II. This step in the procedure was found to be the single most important factor in arriving at reproducible results in the IgM test. The EBV IgM antibodies from our results to date with this method in 14 cases of heterophil-positive cases of mononucleosis appear short lived, lasting 2 months or less. These antibodies were found in only 2 of 18 selected non-mononucleosis cases, in both associated with EBV-viral capsid antigen antibody rise or seroconversion. The successful elimination of nonspecific fluorescence by a simple, inexpensive procedure and the possibility of testing unabsorbed, unfractionated sera directly will facilitate the use oe the EBV IgM antibody test in the future.