Comparative performance of four methods (IFI, IgM anti-VCA, Organon Teknika; ELISA, IgM anti VCA, Incstar Corp and Pharmacia Diagnostic Inc; ELISA IgM against a group of several antigens which principal component is EBNA, Behring Institute) to detect antibodies (Abs) against Epstein-Barr virus in 180 patients (group 1) with infectious mononucleosis with no heterophil Abs (Organon Teknika), 180 healthy subjects with no heterophil Abs (group 2) and 20 patients with infectious mononucleosis (group 3) and with positive heterophil Abs, were studied. In group 1, 10% of patients had IgM Abs, without differences IgM Abs. In group 3 all patients had IgM Abs with no differences in the methods studied. There were no differences in the performance of the evaluated methods to detect IgM against different antigens, but those which use a group of antigens from the virus could be more useful in patients immunologic disorders.