A Japanese scientist behind a seemingly groundbreaking stem cell study says the findings should be withdrawn amid doubts over its quality.
It was reported in January that dipping cells in acid could cheaply and quickly convert them into stem cells.
But questions were raised about the images used in their scientific report and other research groups have failed to reproduce the results.
Prof Teruhiko Wakayama said: 'It is no longer clear what is right.'
The future of regenerative medicine is pinned on stem cells, which can transform into any other type of tissue. They are being investigated for restoring sight to the blind and repairing the damage caused by a heart attack.
'Mistakes have emerged'
The original study, published in the journal Nature, became a huge story around the world and was described as 'remarkable' and as a 'major scientific discovery'.
It said stem cells no longer needed to be taken from embryos or made by complicated and costly genetic tinkering.
Instead shocking skin cells with acid could drive them back into a stem cell state.
The breakthrough findings have not been discredited, but they have come under intense scrutiny.
The Reuters news agency reports Prof Wakayama, University of Yamanashi, told Japanese TV: 'When conducting the experiment, I believed it was absolutely right.
'But now that many mistakes have emerged, I think it is best to withdraw the research paper once and, using correct data and correct pictures, to prove once again the paper is right.
'If it turns out to be wrong, we would need to make it clear why a thing like this happened.'