The interest in infectious mononucleosis stimulated by the work of Paul and Bunnell1 continues to increase, as is shown by the number of publications on the subject that have appeared since these investigators established a serologic test for diagnosing the condition.
In a previous report2 the clinical and cytologic aspects of the disease were reviewed. Serologic analyses of the serums of thirteen patients were given, and the nature of the sheep cell antibodies in the blood of these patients was discussed. A modification of the test originally devised by Paul and Bunnell was introduced as an aid in the diagnosis of borderline cases. This modification has eliminated or confirmed suspicious clinical observations in many cases but has failed to do so in others. The serologic diagnosis of infectious mononucleosis in the early stages of the disease or when there is mild involvement is frequently hampered by the presence