"We have been on a hunger strike for three days," Saddam declared as the trial resumed for its 12th hearing since it opened in October.
His fellow defendant and half brother Barzan al-Tikriti said he had been on hunger strike for two days.
In another session yet again marked by outbursts, testimony was heard from three former regime officials.
The trial has been adjourned until February 28.
Heated exchanges between the defendants and presiding Judge Rauf Abdel Rahman again marked the start of the hearing.
Justice Abdel Rahman, a Kurd, has taken a tough line against the defendants' courtroom behaviour after his predecessor resigned in January.
As the judge pounded his gavel to restore order, Saddam told him to "take that hammer and knock yourself on the head."
Witnesses testify
The first witness, an anonymous former member of the intelligence services, testified from behind a curtain to protect his identity.
He claimed he had only been a minor official at the time of the 1982 massacre of Shiites in the village of Dujail, over which Saddam and his co-accused face charges.
During cross-examination, defendant Barzan asked the witness a few questions, then launched into a long speech denying any connection to the massacre.
"Over the last few sessions, I have become convinced that all the people testifying against me are doing so just because I'm Saddam's brother," he said, adding that he had only been questioned for four hours about the case after spending three years in custody.
"Slow justice is tyranny," he said.
When the judge tried to cut short Barzan's long speech, he asked the judge: "Why are you always so angry? You are like a train with a full head of steam".
The second witness, Fadel Selfij al-Azzawi, also a member of the intelligence service and a former ambassador to Moscow, also denied any knowledge of the case and said he was testifying against his will.
The final witness, former minister of culture Hamad Yussef Hamadi, was Saddam's personal secretary at the time of the Dujail massacre, but like the others claimed he had been forced to testify.
Prosecutors also presented a letter signed by Barzan dated two weeks after the events and addressed to Iraq's leadership praising the intelligence investigation team in Dujail for their efforts in rounding up suspects, but Barzan cast doubt on the letter's authenticity.
Mr Hamadi was shown a piece of paper recommending rewards for six officials for their part in the Dujail arrests, bearing the hand-written word "agreed".
He said the handwriting looked like that of "President Saddam".
Barzan was ejected from the court on January 27, prompting a walkout by the entire defence team and a boycott of the next session of the trial by all of the defendants.