Adenosine Deaminase (ADA) is an enzyme which is mainly involved in purine metabolism and is very much needed to breakdown Adenosine from food and maintain turnover of nucleic acid in tissues. Studies carried out in the past on the clinical usefulness of ADA has predicted its application in the diagnosis of variety of infectious diseases such as tuberculosis, typhoid, Infectious mononucleosis and certain malignancies especially those of haematopoietic origin. ADA levels in patients with pneumonia caused by M.Pneumoniae and Chlamydia Spp were found to be sensitive in diagnosing a particular type of infection. This review article summarises some important clinical usefulness of ADA measurement in body fluids.