Sinn Féin's Pearse Doherty appears to be on target to win the Donegal South West by-election.
Fianna Fáil's vote in the Constituency has dropped by more than half, creating a major headache for Brian Cowen as his government prepares to deliver a budget.
Fine Gael's candidate Barry O'Neill is conceding defeat to Sinn Féin.
Labour leader Eamon Gilmore is denying that his party has had a poor showing, saying Frank McBrearty did three times better than the party's previous performance in the constituency.
The result of the first count is imminent.