Voters are heading to the polls in Oldham East and Saddleworth in the first by-election test of the new parliament.
The by-election was called after an election court declared last year's contest void after finding that Labour victor Phil Woolas had made false statements about the Lib Dem candidate Elwyn Watkins.
Prime Minister David Cameron has been repeatedly forced to deny that the Tories have run a half-hearted campaign in the by-election in a bid to bolster their Lib Dem coalition partners. He visited the constituency to join the campaign trail.
Deputy Prime Minister Nick Clegg, the Lib Dem leader, and other Lib Dem ministers have paid numerous visits to the constituency to try to shore up their vote.
Labour leader Ed Miliband has also visited the constituency.
The result is expected in the early hours of Friday.
The full list of candidates in alphabetical order are: Debbie Abrahams (Labour); Derek Adams (British National Party); Kashif Ali (Conservative); Peter Allen (Green Party); David Bishop (Bus-Pass Elvis Party); The Flying Brick (Monster Raving Loony Party); Loz Kaye (Pirate Party of the United Kingdom); Stephen Morris (English Democrats); Paul Nuttall (UK Independence Party); Elwyn Watkins (Liberal Democrats).