People voluntarily amend and update information on Wikipedia
Online encyclopaedia Wikipedia "lost" 49,000 of its volunteer editors in the first three months of 2009, University research suggests.
The figure compares with a loss of 4,900 over the same period in 2008.
The encyclopaedia-style website encourages editorial changes from everybody who comes to the site.
Wikimedia UK, a chapter of the organisation that operates Wikipedia, has denied that it means the site is struggling.
It says that it is seeking more expert contributors.
"We're trying to engage a bit more at the moment with people who are very knowledgeable, people who are experts, so working with museums was the obvious next step," said Michael Peel of Wikimedia UK.
"Wikipedia is definitely not dying. It's freely licensed which means that content that has been added will be there forever," he added in an interview with The Times newspaper.
The research was carried out by Felipe Ortega, from the Universidad Rey Juan Carlos in Madrid.
Mr Ortega said that if the downward trend continued it could spell problems for the site.
"If the negative trend is maintained for too much time, say one or two years, eventually the project could enter a problematic phase," he said.