Alistair Darling has taken the plunge and accepted a challenge from James McAvoy to take part in the ice bucket challenge.
The Better Together leader posted a picture of himself being drenched in icy water after he and First Minister Alex Salmond were nominated by the Scottish actor.
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The social media craze is aimed at raising awareness and money for the neurodegenerative disease ALS, or motor neurone disease.
Mr Darling thanked McAvoy and tweeted a link to www.gordonsfightback.com, an awareness-raising site set up by Better Together director of research Gordon Aikman.
Mr Aikman publicly revealed he is dying of the disease in a powerful article in the Scotland on Sunday newspaper in June.
The First Minister has also accepted McAvoy's challenge.
Mr Salmond said: "I'm always up for any challenge, and I'm game for this one. It will invigorate me for the next month of campaigning - but the Scottish media should be careful what they wish for, as I get to nominate who's next for the ice bucket!"
In his video, X-Men star McAvoy said: "As it is the year of the Scottish referendum on independence, I'd like to nominate our political champions Alistair Darling and Alex Salmond to do their very worst."
As a bucket of icy water is poured over his head, he adds: "Alex, Alistair, you've got 24 hours."
McAvoy said he was nominated for the challenge by Chelsea manager Jose Mourinho.
Former US president George Bush, actress Gwyneth Paltrow and footballer David Beckham are among a host of well-known faces that have taken the plunge.
McAvoy, from Glasgow, has previously said he is "anti-political" when it comes to independence.
In an interview in May, he said: "I will go with whatever way my country votes, but I don't know which way I want to go yet."