Those who fear blood tests because of the doctor's needle will welcome research showing that saliva tests can also reveal the presence of disease.
Already used to detect drugs and alcohol, it may soon also be used to detect cancers and identify infections.
Scientists involved in the work argue that while the eyes may be the window to the soul, the mouth is the window to the body.
"Nearly everything that is going on in your body reveals itself in some way in the fluids in your mouth, whether it is from saliva, mucous or the plaque on your teeth," said Prof Daniel Malamud.
Prof Malamud, of the Department of Biochemistry at the University of Pennsylvania, Philadelphia, was amongst a group of scientists describing the latest discoveries in saliva-based diagnosis at the AAAS meeting in Washington.
They believe it could revolutionise medical diagnosis and be used to detect a huge variety of substances and organisms present in the mouth. Research has already shown that fluids in the mouth contain drugs, bacteria, viruses, hormones, antibodies, growth factors, DNA and RNA.
Samples from the mouth can already be used to predict how vulnerable a person is to dental cavities, according to Prof Paul Denny of the University of Southern California. He and colleagues developed a test to detect saliva proteins. These have special sugars that attach to the surface of bacteria in the mouth.
There are more than 50 of these sugars and they occur in different combinations from person to person, Prof Denny said.
Certain combinations seem to make people more or less susceptible to the occurrence of cavities and his test shows which patients are more at risk.
Prof David Wong, of the University of California, Los Angeles, has developed a saliva test reported in the journal Clinical Cancer Research that indicates whether a person has head or neck cancers by detecting RNA molecules.
Tests from Prof Malamud's group detect the presence of HIV and a bacterium similar to Anthrax.
A multicentre effort is now underway to identify the entire set of proteins in saliva, its "proteome".
This would allow comparison between a healthy person's protein list and that of an ill person to provide diagnostic targets, Prof Wong argues.