Hossam Badrawi, a reformer and top physician, took the post of head of the policies committee, held by Gamal Mubarak, and that of secretary-general.
On Friday US President Barack Obama urged Mr Mubarak to "make the right decision" and to begin the transition "now", without explicitly saying he should step down.
Opposition demonstrators still occupy Tahrir Square, the main focus of the protests, but their numbers have fallen from Friday's huge rally .
