  New facilities explore warm dense matter (WDM) at extreme conditions where
the densities are very high (e.g., carbon up to density of 50 g cm$^{-3}$) so
that electrons are degenerate even at 100 eV temperature. Whereas in the
non-degenerate region correlation effects such as Debye screening and its
improvements are relevant for the ionization potential depression (IPD), new
effects have to be considered in degenerate plasmas. In addition to the Fock
shift of the self-energies, the bound-state Pauli blocking becomes important
with increasing density. Taking these degeneracy effects into account leads to
a reduction of the ionization potential and to a higher degree of ionization.
Standard approaches to IPD such as Stewart-Pyatt and widely used opacity tables
(e.g., OPAL) do not contain Pauli blocking effects for bound states so that
they fail to explain experiments with WDM in the high density region. As
example, results for the ionization degree of carbon plasmas are presented.
