We report a theoretical investigation of the frequency response of optical interference filters written in photorefractive materials. Counterpropagating coherent beams interact in the volume of a photorefractive crystal through two-beam coupling. The resulting hologram is fixed. The reflectivity of the hologram is calculated as a function of frequency. An analytic solution is obtained for arbitrary grating phase ? in the lossless case, α = 0. Numerical solutions are performed for α > 0. Experimental results are compared favorably with the theory.