Veteran independent MSP Margo MacDonald, who has Parkinson's disease, has told fellow politicians that she wants the right to end her own life.
Margo MacDonald says the terminally ill should have choices
Speaking in a Scottish Parliament debate, Ms MacDonald claimed she should have the right to "assisted death" if her condition deteriorated.
Palliative care was not always effective, she added, and the dying should be given choices.
Health Secretary Nicola Sturgeon said there were no plans to change the law.
In the members' debate on choices for patients coming to the end of a terminal illness, called by Lib Dem MSP Jeremy Purvis, Ms MacDonald said assisted dying should be legalised.
"I would like to have the right to determine by how much my capacity to fulfil my social function, my familial functions, my personal functions is going to be truncated," she added.
The MSP for the Lothians region added: "I don't want to burden any doctor. I don't want to burden any friend or family member.
"I want to find a way in which I can take the decision to end my life in case I'm unlucky enough to have the worst form of Parkinson's near the end of life."
Mr Purvis also called for the law to be changed to allow terminally people to be allowed to ask for assistance to die as they approach the end of their life.
He said: "The time is right for the parliament to be able to hold a full and open inquiry into choices that people can and should be able to make at the end of a terminal illness."
However Ms Sturgeon said the government's focus should instead be on providing quality palliative care for all.
"Our aim must be to ensure palliative and end of life care will be provided for everyone who requires it, regardless of diagnosis, to ensure quality of life for patients, their carers and families, and to ensure that people do not suffer unbearably during the final stages of their lives," she added.