The leader of South Africa's governing ANC is at the Constitutional Court to try to prevent prosecutors using some evidence against him.
Jacob Zuma's lawyers argue his constitutional rights to privacy were violated when investigators raided his home three years ago.
They seized evidence, allegedly linking him to corruption - which he denies.
As African National Congress leader, Mr Zuma is the strong favourite to succeed Thabo Mbeki as president in 2009.
But Mr Zuma's ambitions could be thwarted by a second trial on corruption charges which is scheduled for August this year.
The 65-year-old has said he would only resign if a court found him guilty.
Politically motivated
The BBC's Peter Biles in Johannesburg says Mr Zuma looked relaxed as he arrived at the court where there was a heavy police presence outside.
JACOB ZUMA
Photographers were ushered out of the courtroom after Mr Zuma shook hands with his attorney and the chief executive of Thint, a French arms company, and took a seat behind two rows of lawyers.
Prosecutors allege Mr Zuma accepted bribes from Thint to halt inquiries into a 1999 $5bn arms deal.
Mr Zuma was the country's deputy president before being fired in 2005 when his financial adviser, Schabir Shaik was found guilty of soliciting bribes and jailed for 15 years in connection with the arms deal.
The raids being contested by Mr Zuma took place at his two properties and his lawyer's office in Durban in August 2005 - two months after Mr Shaik was found guilty.
Mr Zuma was then put on trial, but the case collapsed in 2006 when the prosecution said it was not ready to proceed - a court had ruled that documents obtained during the raids could not be used by prosecutors because the search warrants used by police were illegal.
Last year, the Supreme Court upheld appeals against this ruling, saying that the tens of thousands of pages of seized documents could be used in evidence.
The ANC leader and Thint are challenging this.
Mr Zuma has vehemently denied the corruption charges, and argues that the case is politically motivated.
Poisoned letter
Just after his election as ANC president in December last year, the National Prosecuting Authority (NPA) charged him with corruption, fraud, racketeering and money laundering.
On Monday, it emerged that a letter containing poison had been sent to South Africa's chief prosecutor.
The NPA's Mokotedi Mpshe did not touch the letter himself but five of his staff are being treated after developing rashes and his office was sealed off.
Mr Mpshe was appointed to head the NPA last year when his predecessor was sacked by President Thabo Mbeki.
The NPA has been embroiled in accusations of political dirty tricks over its pursuit of Mr Zuma.
The ruling ANC has called for the Scorpions unit of the NPA to be disbanded in June - two months before Mr Zuma is due to go on trial.
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