Scientists believe they have identified thousands of genes which appear to play a role in chronic fatigue syndrome.
No test currently exists for chronic fatigue syndrome
A team from Glasgow University found a particular pattern of genetic activity among 50 people with the condition.
They hope their work, which is still in its early stages, could lead to a diagnostic test and new treatments.
CFS - or myalgic encephalomyelitis (ME) - used to be dismissed as "yuppie flu" and has been widely recognised as a disease only in recent years.
Lead researcher Dr John Gow said: "It is another year's development before it becomes an accepted diagnostic test and, similarly, we need to do some trials with therapy before that becomes widely available. But it is exciting."
By looking at the whole genome of about 50 people with chronic fatigue syndrome, they discovered certain genes that were different to those seen in healthy people of a similar age and sex.
Dr Gow said: "We have identified genes which were up-regulated compared with genes in normal healthy individuals, suggesting we could possibly have a diagnostic test for this syndrome which doesn't exist at the moment."
But he said they needed to check that this "gene signature" was specific for chronic fatigue syndrome by looking at more people with the condition, which would take a year or so.
Colleagues at the same university are also looking at targeting treatments towards the faulty biochemical pathways caused by the overactive genes in chronic fatigue syndrome.
These drugs are already on the market for other conditions, so if they are proved to be useful in chronic fatigue syndrome, they could be given to patients in the near future.
"Our work has given us clues as to which pathways are up- or down-regulated and we know which drugs activate different pathways, so we think we can find drug treatments that will be beneficial to patients," Dr Gow said.
"Having said that, it really needs to go through proper trials before these drugs become widely available."
A spokesman from Action for ME said: "We are very interested to know and explore more."
He said it was good that work such as this was being carried out into chronic fatigue syndrome.
The ME Association said the researchers were looking for and needed more funding to continue with their studies.
They partly funded the research.