  We discuss the dependence of observables on the chemical potential in 't
Hooft's large-N QCD. To this end we use the worldline formalism to expand the
fermionic determinant in powers of 1/N. We consider the hadronic as well as the
deconfining phase of the theory. We discuss the origin of the sign problem in
the worldline approach and elaborate on the planar equivalence between QCD with
a baryon chemical potential and QCD with an isospin chemical potential. We show
that for C-even observables the sign problem occurs at a subleading order in
the 1/N expansion of the fermionic determinant. Finally, we comment on the
finite N theory.
