An experimental and numerical study has been performed to evaluate the effectiveness of steady injection flow control for the reduction of losses in the return channel of a radial compressor. This investigation formed part of an overall attempt to develop a strategy for reducing the diffusion ratio of radial compressors. It is envisaged that this flow control would be activated at off-design conditions, where separation levels on the return channel vanes are considerable. A novel radial compressor sector test rig, supported by a blow-down facility and equipped with a range of instrumentation, was used for the experimental portion of the study. This allowed multiple flow control configurations to be studied in a simplified environment. A set of exchangeable, inlet guide vanes provide the test vanes with the correct inlet three-dimensional flow-field, while airfoil static pressure taps allowed the blade loading to be assessed. The numerical portion of the study was conducted using 3D-computational fluid dynamics (CFD) and involved simulations of both the sector test rig and a “substitute system”. In this paper, the rationale for the inclusion of flow control in a radial compressor return channel is discussed. The sector test rig is then described, including the implementation of flow control. The results of the matrix of flow control experiments are then discussed with comparison to the numerical results.