UK scientists are developing a blood test which may be able to pick up signs of Alzheimer's disease before people start to show symptoms.
The test may allow signs of dementia to be picked up earlier
The team from the Institute of Psychiatry found levels of two types of protein in the blood were only present if people had the condition.
The study was published in the scientific journal Brain.
Alzheimer's researchers said being able to diagnose the condition would mean treatments could be given much earlier.
It is currently difficult to diagnose dementia, which affects around 750,000 people in the UK.
Researchers compared protein levels in the blood of 500 Alzheimer's sufferers and compared them with healthy older people.
They used a process called proteomics - the study of proteins - and found that those with Alzheimer's had greater levels of certain proteins in their blood than healthy people.
Professor Simon Lovestone, from the Institute of Psychiatry at King's College London, who led the study, said: "This is definitely good news.
"We found some evidence that there are protein differences in the blood of people with Alzheimer's. "This raises the prospect of a blood test for Alzheimer's disease."
Professor Lovestone said further research was needed to confirm their findings.
Early treatment hope
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "We are delighted to be funding what could be a breakthrough study in the diagnosis of Alzheimer's."
Professor Clive Ballard, director of research at the Alzheimer's Society, said: "As new treatments that target the early stages of Alzheimer's disease are developed, it is very important that we find a way of diagnosing this disease as early as possible.
"Although there have been promising developments in spinal fluid analysis and specialised brain scanning, there is currently no simple way of diagnosing Alzheimer's disease until clinical symptoms emerge.
"A blood test could help people receive treatments before symptoms develop, allowing doctors to give patients treatment that can help stabilise a person¿s condition much earlier."
He added: "Research is still in the early stages and more funding is now needed to ensure that this important research can be done as quickly as possible."