Two genetically different related forms of human immunodefficiency virus (HIV), a human lentivirus belonging to the lentivirus family, called HIV-1 and HIV-2, have isolated from patients with AIDS. HIV can be transmitted through contaminated blood and blood products; from a mother to her offspring during pregnancy, childbirth or breast feeding; or through sexual contact. Sexual transmission remains by far the predominant mode of transmission. Vertical and blood borne transmission of HIV are highly predictable and very efficient modes. Sexual transmission of HIV, however, appears to be considerably less efficient and highly variable. During the early period after primary infection with HIV widespread of dissemination of the virus and a sharp decrease in the number of CD4+T cell count occurs. The use of CD4 cell count is an important indicator of disease severity of AIDS. The patients infected with AIDS can be attacked by various opportunistic infections such as pneumonia, Mycobacterium avium complex, cytomegalovirus, microsporidiosis and tuberculosis. The degree of intensity of these diseases can be indicated by measuring the level of enzyme like alkaline phosphatase, alanin aminotransferase and aspartate aminotransferase, lactate dehydrogenase and creatine phosphokinase.