It is becoming increasingly apparent to investigators and clinicians in a variety of disciplines that saliva has many diagnostic uses and is especially valuable in the young, the old and infirm and in large scale screening and epidemiologic studies. The highly sensitive test procedures that are now commonplace makes it practical to quantitate, despite very low concentrations, a large number of hormones and drugs in saliva. Indeed, all steroids of diagnostic significance in routine clinical endocrinology can now be readily measured in saliva. Drug monitoring can include abusive as well as therapeutic agents. The concordance between anti HIV antibodies in saliva and serum has stimulated application to various other antiviral antibodies as well as to viral antigens per se. Saliva has found use as a diagnostic aid in an increasing number of clinical situations and in systemic diseases that can affect salivary gland function and composition such as Sjögren's syndrome, cystic fibrosis and diseases of the adrenal cortex. The list keeps growing.