IgM antibodies specific for Epstein-Barr virus in infectious mononucleosis without heterophil antibodies.

IgM antibodies specific for Epstein-Barr (E.B.) virus were demonstrable in all but one out of 46 patients diagnosed as having infectious mononucleosis wihout heterophil antibodies; cytomegalovirus aetiology was excluded. In all but two cases the highest titre was found in the first sample. In 21 patients a significant decrease was seen within a few weeks. IgG antibodies to E.B. virus, mostly remaining at a constant level, were demonstrable in all cases. IgM antibodies to E.B. virus were found in only five out of 300 controls.The results suggest that in a disease similar to infectious mononucleosis without heterophil antibodies testing of transient E.B. virus-specific IgM antibodies makes a rapid aetiological diagnosis possible and that in clinically well-defined cases viruses other than E.B. virus and cytomegalovirus are unlikely to be causal agents.