The new Lebanese government has replaced several pro-Syrian security chiefs and the public prosecutor.
The appointments came two days after Syrian troops withdrew
The move was a key opposition demand following the assassination of former prime minister Rafik Hariri.
Information Minister Charles Rizk announced the changes after a weekly cabinet meeting, two days after Syria said it had withdrawn all its troops.
A UN team in Damascus is attempting to verify the withdrawal of Syrian troops, assets and intelligence.
UN Secretary General Kofi Annan has said he cannot confirm the withdrawal until these checks are completed.
Mr Rizk said Judge Said Mirza would replace Adnan Addum as public prosecutor.
Gen Ashraf Rifi would replace Gen Ali Hajj at the head of the internal security forces, while Gen George Khoury would take Gen Raymond Azar's place as head of army intelligence, he added.
He said a new head of state security would be announced at a future cabinet session.
And the cabinet postponed a decision on naming a new head of the general security department to replace Gen Jamil al-Sayyed, who resigned earlier this week because of what he described as the changing political scene.
The resignations came as Lebanon prepares for several rounds of elections, beginning on 29 May, which will be the first without a Syrian occupying force for 33 years.
The vote was announced after the government won a confidence vote in parliament on Wednesday.