The Malaysian opposition leader, Anwar Ibrahim, has appeared in court to face charges of sodomy for the second time in a decade.
Dozens of supporters greeted Mr Anwar's arrival in court, before the case was adjourned to allow defence lawyers to gain access to prosecution evidence.
Mr Anwar denounced the court proceedings as the "machinations of a dirty, corrupt few".
He could face up to 20 years in prison if convicted.
Mr Anwar - a former deputy prime minister until his sudden sacking in 1998 - served six years after an earlier sodomy conviction, but led the opposition to election gains in 2008.
He represents a major challenge to Prime Minister Najib Razak, whose coalition has held power for more than 50 years.
Mr Anwar was accompanied by his wife and two daughters as he entered the courtroom. Dozens of his supporters shouted "reform, reform".
The 62-year-old former deputy premier has consistently maintained that the charges against him are a political conspiracy.
In an interview with the BBC before the trial, Mr Anwar said: "I think from the very start we'll state our position and fight it out, and expose their nasty conspiracy.
"We were committed to a reform agenda. We are committed to democratic ideals and some of us may have to pay the price.
Roger Hardy, BBC Islamic affairs analyst
Anwar Ibrahim's political journey has taken him from charismatic student leader to deputy prime minister and now his country's most prominent opposition politician.
He is a formidable political campaigner because of his popular appeal and because he has succeeded in putting together a coalition that straddles Malaysia's ethnic divisions.
This could be a make-or-break moment in Mr Anwar's tempestuous career. But for the current prime minister, Najib Razzak, putting him on trial is a politically risky strategy.
"The image of the country is severely damaged by their actions, and I think they should not underestimate the strength and wisdom of the Malaysian people."
Government officials deny there is any plot against him.
The sodomy allegations have been levelled by a 24-year-old male former aide.
On Friday, the Federal Court upheld a lower court's ruling that Mr Anwar could not have access to medical evidence held by prosecutors.
Mr Anwar's lawyer said the refusal had had "an emasculating effect in our preparation of the defence".
Rights groups have criticised the trial. Amnesty International accused the government of using "the same old dirty tricks in an attempt to remove the opposition leader from politics".
There were huge protests after Mr Anwar's first conviction for sodomy a decade ago. He was freed on appeal in 2004.
All homosexual acts are criminal in Malaysia.
The court is due to reconvene on Wednesday morning.