The fact that infectious mononucleosis is reported chiefly from institutional groups suggests that its recognition in private practice is not common. This is to be expected because of the benignity of the disease and its similarity to relatively brief systemic infections which may not suggest the necessity of making supplementary leukocyte and differential blood counts. This disease entity will be commonly recognized only when its symptomatology becomes of interest to the clinician and when its characteristic lymphocytic blood reaction can be demonstrated with a fair degree of regularity. The statements (which will be challenged) of such competent hematologists as Kracke and Garver1that morphologically the disease cannot be distinguished with certainty from acute lymphatic leukemia emphasize the need for a survey of recent reports. The present paper is based on data acquired over a period of twelve years. Although it may be presumptuous to speak of a disease