Former Argentine President Nestor Kirchner has announced he will resign as the head of the country's ruling Peronist party, reports say.
The move follows a heavy loss for the party in mid-term elections.
Mr Kirchner finished second in a high-profile race during Sunday's vote, defeated by a millionaire from a rival faction within the party.
His wife, President Cristina Fernandez, whose economic policies were unpopular, also lost her majority in Congress.
Mr Kirchner said: "In a democracy, you win and you lose. This was a very close election. We lost by a bit."
Resigning from his position, he said he preferred more political mobility and it was the most dignified thing to do.
His ally Buenos Aires governor Daniel Scioli succeeded him.
Correspondents say Sunday's mid-term polls were seen as a referendum on the presidential couple who have dominated Argentine politics for the past six years.
Cristina Fernandez, who succeeded her husband as president in late 2007, has seen her popularity fall amid the country's worsening economic problems.
She brought forward the elections, which were originally set for October, arguing that this would then allow the country to unite to face the global economic crisis.