By Martin Hutchinson
BBC News Online health staff in Madrid
The fluid that surrounds a developing baby in the womb may be a rich source of stem cells for use in medical research, say scientists.
Stem cells can turn into different types of tissue
Stem cells are the body's "master cells" - capable of growing, as they do within a foetus, to produce every different kind of cell in the body.
Although research is at its early stages, experts hope that one day these cells will help doctors find treatments or even cures for many diseases in which "irreplaceable" cells in the brain or elsewhere are damaged - such as in type I diabetes, Alzheimer's disease or Parkinson's disease.
The principal source of good quality stem cells is currently the human embryo. However, the use of cells from this source is highly controversial - so the possibility of an alternative source will be welcomed by researchers.
Other sources discovered in adult tissues have proved problematic - often these cells are not capable of forming as wide a variety of cell types as experts wish.
What scientists want are the "pluripotent" stem cells - very early cells which have the capability to "differentiate" in stages into a huge number of different types of human cell.
A team from the University of Vienna have found a small group of cells within amniotic fluid - which fills the sac around the developing foetus - which they suspect are pluripotent stem cells.
The cells produce a chemical - called Oct-4 mRNA - which is used by the body to maintain pluripotent stem cells, but disappears rapidly once the cells have differentiated into a less useful versions.
Professor Markus Hengstschlager, who led the research, said: "The question for the future will be - what can these cells do, in which directions can they be differentiated?
"Whether these cells have the same potential as embryonic stem cells is a question that can only be answered by a variety of experiments.
"We believe that our findings, together with the recent demonstration that amniotic fluid can be used for tissue engineering, encourages the further investigation of human amniotic fluid as a putative new source of stem cells with high potency."
However, Professor Benjamin Reubinoff, a stem cell researcher from the Hadassah Medical Center in Jerusalem, said that it was likely to be some time before research into so-called adult stem cells would reveal whether they had the same properties as embryonic stem cells.
He told BBC News Online: "At this point there is no indication that, in the near future, we are going to be able to replace human embryonic stem cells.
"Research into adult and embryonic stem cells should continue in parallel - and the public needs to support that."