The chemicals and compounds present in a person's breath should help spot signs of conditions such as diabetes, cancer, hepatitis and cirrhosis of the liver, they seem to believe.
Using the latest technology the team at Swansea University is trying to develop a paper strip on which patients could breathe, which would show doctors if they are suffering from a certain disease.
If successful, it could save thousands of lives because an early diagnosis tends to increase the chances of survival.
But no trials have yet been carried out, and the team warns that it could take years before the test reaches the NHS.
Research leader Dr Masood Yousef said he was looking at ways to detect the presence of 'volatile organic compounds' - airborne chemicals in the breath.
'Studies have shown that high concentrations of certain volatile organic compounds in breath can correlate with disease,' he added.
'Different chemicals in an analysis of breath can make out particular types of cancer, diabetes, hepatitis and cirrhosis of the liver.'
Diagnostic techniques based on exhaled breath are much less developed than the analysis of blood or urine because any compound is present in such small quantities that it is difficult to detect.
The scientists are looking at complex detection methods such as electronic recognition of gas particles, identifying individual particles by their different atomic weights and using heat to separate the particles from other compounds, Daily Mail reports.
Dr Yousef said: 'If unique markers for specific diseases can be recognised earlier than traditional techniques, then there is immense potential to revolutionise early disease diagnosis before any symptoms have developed, and without the need for invasive procedures.
'Breath samples are much easier to collect than blood and urine, for the patient as much as for the person collecting the sample.
'They can be collected anywhere by people with no medical training, and there are no associated biohazard risks.
'Overall, the procedure is likely to be much more cost effective than conventional methods, potentially saving a great deal of time and money.'
He hopes his research will lead one day to simple diagnostic tools such as test strips that indicate specific illnesses.
Dr Julie Sharp of Cancer Research UK said universities around the world were looking at ways to develop workable breath tests.
'A test that is quick and easy to do would be very welcome, but these breath tests are still being developed and will need thorough testing in large numbers of people before they can be used to routinely screen for cancer,' she said.
Last year, American scientists developed a breath test to pick up the early stages of lung cancer. They found it accurately detected.