Mr Bignone is accused of holding ultimate responsibility for rights abuses
The trial has begun of Argentina's last military ruler, Reynaldo Bignone, and five other retired generals.
The men are charged in connection with the alleged kidnapping, torture and disappearance of 56 opponents of the military government in the late 1970s.
The abuses are alleged to have taken place at the Campo de Mayo base on the outskirts of the capital, Buenos Aires.
Human rights groups say up to 30,000 people were killed or disappeared in Argentina between 1976 and 1983.
All of the eight accused, including two former military government officials, deny the charges.
Mr Bignone, 81, appeared frail and rocked back and forth in his chair as the charges were read out, correspondents said.
"This is a historic trial in the search for truth for all of those who disappeared," Alcira Rios, a lawyer for relatives of one of the victims, told Reuters news agency.
"We have to say no to impunity. We owe it to our Argentine society."
The other retired generals on trial are Santiago Omar Riveros, Eugenio Guanabens Perello, Jorge Garcia, Fernando Exequiel Verplaetsen and Carlos Alberto Tepedino.
More than 130 witnesses are expected to be called to testify against the defendants. The trial is not expected to finish before February.
Mr Bignone, who has been living under house arrest, faces charges in connection with alleged torture, illegal break-ins and human rights violations from 1976 to 1978.
He was the last of Argentina's four military presidents, serving from 1982-83, and handed power over to democratically elected leader Raul Alfonsin when the dictatorship collapsed in 1983.
An estimated 5,000 prisoners were held at the Campo de Mayo barracks, one of the largest death camps in operation during the dictatorship, according to human rights groups.