The photoinduced isotropic and anisotropic changes in the refractive index of dye/polymer guest‐host systems are investigated. The values obtained are compared to the diffraction efficiencies of scalar and polarization holographic gratings, recorded in the same polymer systems. It is concluded that the induced anisotropy is related to the dye molecules involved in the photoprocesses, whereas the isotropic changes, which are much stronger, are related to the polymer matrix as well. ©1995 American Institute of Physics.