  I consider Pauli-Villars' regulators for the ghosts in the path-integral
string formulation and show how they preserve conformal invariance. I calculate
the regulator contributions to the effective action and to the central charge
and demonstrate the consistency of the mean-field quantization of the
Nambu-Goto string in $2<d\leq26$. The higher-derivative corrections to the
Liouville action are briefly considered for the Pauli-Villars and proper-time
regularizations.
