As a diagnostic fluid, saliva offers distinctive advantages over serum because it can be collected non-invasively by individuals, even by patient. Does not require special equipment for collection and storage as unlike blood saliva does not clot. Advantageous for person in whom blood drawing is difficult as in obese and haemophilic patient. Whole saliva used for diagnosis of systemic diseases, because it contains serum constituents. These constituents are derived from the local vasculature of the salivary glands and gingival cervicular fluid.This review examines the diagnostic application of saliva for hereditary disorders, autoimmune diseases, malignant and infectious diseases, and endocrine disorders, as well as in the assessment of therapeutic levels of drugs and the monitoring of illicit drug use, and also for forensic evidence and others. . In future we are likely to see the increased utilization of saliva as a diagnostic fluid. As we enter the era of genomic medicine, sialochemistry will play an increasingly important role in the early detection, the monitoring and progression of the systemic and oral diseases.