Two doctors' groups have dropped their opposition to a proposed change in the law to allow them to help terminally ill patients to die.
Some countries allow assisted dying but there is a ban in the UK
The Royal College of GPs (RCGP) and Royal College of Physicians (RCP) have adopted neutral stances to the Assisted Dying for the Terminally Ill Bill.
The RCP said it no longer opposed the bill because of amendments introduced, including better safeguards.
The RCGP also said it was neutral but added more clarity was still needed.
The private members bill, introduced by Lord Joffe, is currently before the House of Lords Select Committee.
It proposes a lifting of the UK ban to "enable a competent adult who is suffering unbearably as a result of a terminal illness to receive medical assistance to die at his/her own considered and persistent request".
The UK law was last examined in 1994 but a change was rejected.
Since then Belgium, Holland and Oregon have changed their laws to permit assisted dying in different ways.
Professor Raymond Tallis, the RCP's ethic issues in medicine committee chairman, said: "The ethical issues raised by the bill are for society to consider.
"We feel our role is to advice on clinical issues. But we do not think a change in the law should be a substitute for good palliative care."
He said there were still issues to do with doctor training and patient diagnosis which needed to be cleared up.
He also admitted the college's members would not be able to reach an unanimous decision.
The college first opposed the bill in its original version last year.
Dr Ivan Cox, RCGP spokesman on euthanasia, said: "Like society as a whole, many GPs have moved from a position of outright opposition to a more measured agnostic stance.
"Evidence coming from the Netherlands and Oregon, where assisted suicide is now legal, is providing food for thought in UK.
"However, we would like to see clarity on what is meant by terms such as unreasonable suffering and what type of doctor will be expected to carry out these assisted suicides."
The British Medical Association, which represents 120,000 doctors, said it was still opposed the bill.
The move by the colleges was welcomed by the Voluntary Euthanasia Society.
A spokesman said: "It is momentous. It shows medical opinion is changing. Doctors are beginning to look at issues more carefully and consider them on their merits.
"I think a lot of doctors do support the proposals."
But Julia Millington, the political director of the ProLife Party, which opposes a change in the law, said: "It is impossible to put adequate safeguards in place to stop abuses and the boundaries will expand.
"It is alarming that doctors are not coming out clearly in support of preserving the current position."
A recent poll of 100 MPs, commissioned by the ProLife Party, found four in five would oppose a change in the law to allow voluntary euthanasia.