Hosni Mubarak's defence lawyer was likely to inflame Egypt's democracy protesters by claiming in court that the ousted leader was still president.
Mubarak's lawyer, Farid el Deeb, made the claim when he said that Mubarak's trial in a criminal court violated the country's suspended constitution.
"This court is not qualified to try him and he must be acquitted," Deeb said.
His argument was rejected by legal experts who insisted it was likely to be dismissed by Judge Ahmed Refaat.
Protesters and lawyers of the families of those killed in the days that led to the ousting of the former leader criticised Deeb's argument as "delusional".
"Mubarak left his position, not by resigning, but because the January 25 revolution forced him out," said Judge Mohamed Hamed el-Gamal, the former head of Egypt's State Council.
"He will be judged by Egyptian law like any other Egyptian because he is not president."
New demonstrations have been organised in Cairo to mark the first post-Mubarak parliament session.
Revolutionaries have warned that they would take to the streets in protest against the Supreme Council of the Armed Forces' tight grip on power.
Tensions between the different political factions, meanwhile, have surfaced. The Egyptian Social Democratic Party has left a power-sharing agreement with the Muslim Brotherhood's Justice and Freedom Party, raising fears that fragmentation would weaken parliament.