It is shown that blazed computer generated holograms having a rotational symmetry (RSH) are especially suitable for interferometers working in reflected light which can be used in testing aspherics. The RSH acts either as a null lens of a very complex kind or it is used not only as beam splitter but also as beam combiner. From a more technical point of view, the latter version is especially interesting although in this case parasitic light caused by the double passage of all beams through the RSH may spoil the interference pattern. The two versions were tested experimentally. So, a Twyman-Green interferometer, on the basis of a blazed RSH, was built and tested. The interference pattern was free from severe disturbances because of the double passage through the RSH. Also a Fizeau interferometer was tested where the RSH acts as beam splitter and reunifer. Here the disturbances were more severe owing to the fact that the zero order as well as one first order of diffraction must be used. Possibilities for the suppression of stray light in this type of interferometer are discussed.