  We study the equation of state of QCD using an improved version of the
three-flavor Polyakov-Nambu-Jona-Lasinio model beyond the mean-field
approximation. It incorporates the effects of unquenched quarks into the
Polyakov-loop effective potential, as well as mesonic contributions to the
grand-canonical potential. We study in full detail the calculation of the
thermodynamical potential in this approach and compare the resulting pressure
and entropy density with the most-recent lattice-QCD calculations at zero
baryochemical potential. Finally, we present some exploratory results at finite
chemical potential which include the phase diagram of the model, the quark and
meson masses, and finally, the thermodynamical pressure.
