  We study various aspects of the Kahler metric for matter fields in N=1,2
orientifold compactifications of type IIB string theory. The result has an
infrared-divergent part which reproduces the field- theoretical anomalous
dimensions, and a moduli-dependent part which comes from N=2 sectors of the
orientifold. For the N=2 orientifolds, we also compute the disk amplitude for
two matter fields on the boundary and a twisted closed string modulus in the
bulk. Our results are in agreement with supersymmetry: the singlet under the
SU(2)_R R-symmetry has vanishing coupling, while the coupling of the SU(2)_R
triplet does not vanish.
