A US appeals court has blocked attempts by the Bush administration to stop Oregon doctors helping terminally ill patients commit suicide.
Lethal prescriptions have been given to over 170 Oregon patients
Attorney General John Ashcroft had ordered doctors in the state not to comply with a law allowing them to prescribe lethal doses of medication.
By a two-to-one decision, judges on the Ninth Circuit Court of Appeals ruled Mr Ashcroft had exceeded his authority.
At least 170 people have used Oregon's law to commit suicide since 1998.
Supporters of the law - officially titled the Death With Dignity Act and twice approved by Oregon voters - cheered as the ruling was read out.
"The attorney general's unilateral attempt to regulate
general medical practices historically entrusted to state
lawmakers interferes with the democratic debate about
physician-assisted suicide," said the judges.
They said Mr Ashcroft's action "far exceeds the scope of his authority under federal law".
Supporters of Oregon's law were delighted with the court's ruling.
"What the law does in Oregon is it brings tremendous peace of mind to terminally ill people who are suffering, who want to spend the last weeks of their life with their friends and loved ones in peace," Scott Swenson, executive director of the Death with Dignity National Center, told Reuters.
Oregon is the only state to allow such lethal prescriptions in the US.
Mr Ashcroft, a conservative Christian, issued his directive in 2001.
In it he declared that using drugs restricted under the Controlled Substances Act to help patients commit suicide was not a legitimate medical purpose.
Assisted suicide in Oregon
Patients must be in final six months of terminal illness
Patients must make two oral requests and one written request to die, each separated by a two-week period
Patients must be mentally competent to make decision
Two doctors must confirm diagnosis
Lethal prescription of drugs prescribed by doctor and administered by patients themselves
He ordered that doctors and pharmacists prescribing lethal doses of drugs should have their prescription licenses revoked.
The appeals court ruling is just the latest step in Mr Ashcroft's campaign against the Oregon law.
His directive has already been blocked by a federal judge, and he is expected to appeal the latest ruling.
In all cases, legal judgements against Mr Ashcroft's directive have rested on his powers, or lack of powers, to interfere in state medical regulation - not on the ethics of euthanasia itself.
"We express no opinion on whether the practice is inconsistent with public interest or constitutes illegitimate medical care," said the judges' ruling.
However, in a voice of dissent, the third judge on the panel, Judge J Clifford Wallace, said he believed in the absence of a clear Congressional policy, Mr Ashcroft's ruling should have been given "substantial deference".
"Certainly, Congress is free to enact legislation limiting or counteracting the Ashcroft directive's effects," Judge Wallace wrote.