Former US Senator Fred Thompson has withdrawn from the Republican presidential race, after a string of poor finishes in early voting rounds.
The actor-politician leaves a Republican race that is wide open
"I have withdrawn my candidacy... I hope that my country and my party have benefited from our having made this effort," he said in a short statement.
It follows his third place result in Saturday's South Carolina primary - a state he had said he needed to win.
Mr Thompson did not say if he would endorse any of his former rivals.
The ex-Tennessee senator ended his statement by saying that he and his wife, Jeri, would "always be grateful for the encouragement and friendship of so many wonderful people".
The actor-politician entered the race in September, months after his rivals had started campaigning.
After climbing into second place in national polls in October, his support steadily plunged as his many critics questioned how seriously he desired the job, says the BBC's Vincent Dowd in Washington.
He finished third with 16% in the South Carolina primary, behind John McCain on 33% and Mike Huckabee with 30%.
The former star of the Law and Order TV series will have thought hard about whether the next Republican primary in Florida at the end of this month offered any hope of a revival - clearly he decided it did not, our correspondent says.
Still wide open
Even with Mr Thompson's departure the Republican race remains wide open, with three candidates each having won in the six states that have voted, our correspondent says.
The remaining Republican presidential contenders are focusing on Florida ahead of that state's primary on 29 January.
Polls suggest Mr McCain has a narrow lead in the Sunshine State over ex-New York mayor Rudolph Giuliani, former Massachusetts governor Mitt Romney and Mr Huckabee.
The Democratic White House hopefuls are gearing up for Saturday's South Carolina primary, a day after Barack Obama and Hillary Clinton clashed in a TV debate.
The two senators continued to trade blows on the campaign trail on Tuesday.
The former first lady claimed Mr Obama had been "looking for a fight", while he repeated his claim that the Clintons had been attacking him in "not accurate" ways.
All the contenders are looking towards the potentially decisive "Super Tuesday" on 5 February, when 22 states will vote for a candidate from either side to stand in November's presidential election.