Mr Menem insists the arms shipments were legal
The former President of Argentina, Carlos Menem, has been formally charged with involvement in arms-trafficking.
Prosecutors said Mr Menem had illegally sold weapons to Croatia and Ecuador in the 1990s, when they were involved in conflicts. He denies the charges.
Mr Menem, who has been ill, took part in the session on a video-link from the northern province of La Rioja.
He governed Argentina from 1989 to 1999. He has been on trial, alongside 17 co-defendants, since October.
He and his co-defendants are accused of authorising the sale of weapons, including rifles, anti-tank rockets and ammunition, to Croatia and Ecuador between 1991 and 1995.
At the time, Croatia was under a UN arms embargo because of its involvement in the violent break-up of the former Yugoslavia, while in 1995 Ecuador was involved in a month-long conflict with neighbouring Peru.
Mr Menem has said he signed the decrees authorising the shipments but maintains they were legal as they were destined for Panama and Venezuela, which were both at peace.
Evidence about the true destinations first came to light in 1995.
In 2001, Mr Menem spent several months under house arrest on similar charges, but he was set free by a panel of judges, most appointed during his presidency.
The case against him was filed again after President Nestor Kirchner, who was in office between 2003 and 2007, replaced all the judges.
If found guilty, Mr Menem could technically face a sentence of up to 12 years in prison.
However, as a serving senator - he represents the western province of La Rioja - Mr Menem is immune from imprisonment.
Prosecutors would either have to wait until his term in office expires, in 2014, or ask the Senate to pass a special motion to put him behind bars, the BBC's Daniel Schweimler in Buenos Aires says.
Mr Menem insists he is the victim of a political campaign by current President Cristina Fernandez, wife of former President Kirchner.