Human Immunodeficiency Virus (HIV) causes damage to the human immune system and the disease known as Acquired Immune Deficiency Syndrome (AIDS). This virus is a member of the Lentivirus group of viruses of the Retrovirus subfamily, which has a reverse tran-scriptase enzyme. HIV infects cells which expres CD4, mediated by gp 120. HIV infection changes the lymphocyte migration pattern, the activity of cytotoxic T cells and CD4 T cell count. The T cell CD4+ count is related to the progressivity of the disease.Anti gp 120 is the antibody most abundantly produced during HIV infection. Spesific antibody concentration for the antigens vary among individuals and single individual at different stages of the infection. Expression of the HIV antigen and/or antibody can be used to establishing the diagnosis and determine the stage of the disease. CD4+ cells count can be used to determine the stage of HIV infection, to predict the occurance of opportunistic infection and other complications, and to determine as well as to monitor therapy