Actor Michael J Fox says he was neither acting nor off his medication in recent US political campaign adverts.
The adverts show Fox, 45, shaking from the effects of his disease while asking voters to back Democrat candidates who support stem cell research.
Conservative radio commentator Rush Limbaugh claimed that the actor was exaggerating his condition.
"That's funny - the notion that you could calculate it for effect, Fox told CBS News. "Would that we could."
"Disease is a non-partisan problem that requires a bipartisan solution"
Election issue
The campaign advert ran in Missouri, where the issue of stem cell research has become an important issue in the mid-term elections.
The actor urges voters to accept an amendment which would change the state constitution to permit federally-approved research on cells derived from human embryos.
He also voices his support for Democratic candidate Claire McCaskill, who supports stem cell research and is challenging Republican Senator Jim Talent for his seat in the state.
"They say all politics is local, but it's not always the case," Fox says in the 30-second advert.
"What you do in Missouri matters to millions of Americans. Americans like me."
Mr Limbaugh criticised the adverts on his radio show, telling listeners that Fox was "really shameless" in his efforts to stir up sympathy.
He later apologised for his comments.
Degenerative disease
Fox told CBS News on Thursday that he was not interested in politics, and had only made the adverts to highlight his pursuit of a cure for Parkinson's.
"Disease is a non-partisan problem that requires a bipartisan solution," he said.
Parkinson's is a degenerative disease of the nervous system that generally affects both men and women who are more than 40 years old.
The disease develops slowly over time and is associated with trembling of the arms and legs, stiffness and rigidity of the muscles and slowness of movement.
Fox was diagnosed with Parkinson's in 1991 and revealed his condition publicly in 1998.
In 2000, he quit full-time acting because of his symptoms and founded the Michael J Fox Foundation, which has raised millions of dollars for research into a cure.
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