The 48 defendants appeared in a packed courtroom in the capital in the latest phase of the trial, which has been condemned by human rights activists. Many of the defendants are accused of inciting violence and violating the constitution during protests over 2005 parliamentary elections.
Former parliamentarian Bedru Adem called two witnesses to testify that he was in prison on the date he was accused of participating in street violence. He also said he was not trying to incite violence when he addressed two pre-election rallies.
"I called upon the people to change the system peacefully, nonviolently, using their voters card," he told the court.
Regarding the charge that he threw rocks at police during a November 2005 riot, he said: "I'm an old person, I'm 50 years old. I have gray hairs and they are saying that I threw rocks. It would've been better if they said I shot guns."
It was not clear how many of the 48 defendants would choose to put on a defense. Thirty-eight of the defendants asked presiding Judge Adil Ahmed to give them the court's list of accusations and evidence before they would agree to defend themselves.
The judge also asked four newspaper owners, who had charges dropped against them as individuals, to defend their organizations. He issued a warrant seeking the identities of two other newspaper owners, who have not yet appeared in court.
The judge then adjourned until Wednesday.
The defendants were charged in December 2005 with treason, inciting violence and attempted genocide. On April 9, the court freed 25 prisoners, among them eight journalists. Earlier in April, the judge dropped the charges of treason and attempted genocide.
The trial has been widely condemned by international human rights groups as an attempt to silence Ethiopian government critics. The opposition leaders have claimed the trial is politically motivated.
The violence erupted during protests over elections that returned Prime Minister Meles Zenawi to power in May 2005. The opposition, despite winning an unprecedented number of parliamentary seats, claimed the vote was rigged, and EU observers said the polls were marred by irregularities.
Late last year, Ethiopia acknowledged that its security forces killed 193 civilians protesting alleged election fraud, but insisted they did not use excessive force. A senior judge appointed to investigate the violence had accused the security forces of excessive force.