Infectious mononucleosisis a viral disease of the lymph system, clinically not so significant because its clinical symptoms are rarely severe with life-threatening serious complications and consequences. Infectious mononucleosis is mild disease; characterized by fatigue, fever, pharyngitis, hepatosplenomegaly, lymphadenopathy and digestive discomfort. The disease affects commonly children and adolescents with low social status and children from developing countries. According to the findings of specific serum antibodies, 95% of children in developing countries get over this infection at pre-school age. Viruses that cause infectious mononucleosis are the Epstein-Barr virus and Cytomegalovirus. They belong to the Herpesviridae family. The most important characteristic of the viruses is that they cause lifelong infections with occasional reactivation periods. Diseases can range from clinically unobserved to malignant tumors such as Burkitt's lymphoma, Hodgkin's and non-Hodgkin's lymphoma, nasopharynges carcinoma, and disease in solid organ or bone marrow transplantation. The most common methods for the diagnosis of infectious mononucleosis are indirect methods(ELISA and ELFA methods). Testing is based on the antibody determination in the patient's serum. In the primary immune response, IgM antibodies occur which indicate an acute infection and can be diagnosed between the first and second week of infection. After the second week, IgG antibodies occur and indicate a past infection. IgG antibodies can be diagnosed any time because they remain in the blood for life. In the secondary immune response, IgG antibodies have a faster and stronger intensity of action than in the primary immune response because they are excreted from the memory cells that have already occurred at first contact with the foreign antigen.