Gordon Brown will campaign in Glenrothes today in his first by-election visit since becoming Prime Minister.
He is expected to visit the constituency to shore up Labour's vote in a fight where the bookies for weeks have made the SNP favourites to win.
Mr Brown's visit comes three days after his wife Sarah went campaigning in the town.
With candidate Lindsay Roy and Scottish Labour leader Iain Gray, she spent 20 minutes knocking doors, many of them sporting Labour posters, in the former mining village of Cardenden.
She gave no interviews in the brief foray, but said beforehand: "We're at home for the half-term and I thought it would be nice to spend some time helping out the campaign this week."
For Labour the Glenrothes contest is fraught with uncertainty, coming only months after the party's sensational defeat in Glasgow East where that seat was captured by the SNP.
The seat fell vacant by the death of John MacDougall, who had a majority over the SNP of 10,664 in 2005.
In Glasgow East, the SNP overturned a Labour majority of 13,507.
And the most recent Westminster parliamentary by-election in Fife saw the Liberal Democrats capture Dunfermline and West Fife from Labour in 2006, overturning a majority of more than 11,000.
Like Glenrothes, that seat was next door to Mr Brown's Kirkcaldy and Cowdenbeath constituency.
Mr Brown did not campaign in Glasgow East, citing the convention that Prime Ministers do not take part in such contests. But the SNP said Tony Blair visited three as Prime Minister - Uxbridge, Eddisbury and Hamilton South.
In Glenrothes, Labour at first deployed the same argument but on October 14 Mr Brown said in a letter to Labour MPs and peers that he and his wife intended to visit the constituency "subject to the global financial situation".
Before the banking and economic crisis, the by-election had been seen as critical to Mr Brown's political future.
But the crisis has overshadowed the contest, and has also given Mr Brown a weapon with which to attack the SNP. He has argued an independent Scotland could not have bailed out its banks.
That has been hotly disputed by the SNP, who argue Labour's stewardship of the economy helped bring about the crisis, and Alex Salmond has challenged Mr Brown to debate with him in Glenrothes.