  We consider perturbative Type II superstring theory in the covariant NSR
formalism in the presence of NSNS and RR backgrounds. A concrete example that
we have in mind is the geometry of D3-branes which in the near-horizon region
is AdS_5 x S_5, although our methods may be applied to other backgrounds as
well. We show how conformal invariance of the string path integral is
maintained order by order in the number of holes. This procedure makes uses of
the Fischler-Susskind mechanism to build up the background geometry. A simple
formal expression is given for a \sigma-model Lagrangian. This suggests a
perturbative expansion in 1/g^2N and 1/N. As applications, we consider at
leading order the mixing of RR and NSNS states, and the realization of the
spacetime supersymmetry algebra.
