High damping rubber (HDR) is used in the manufacturing of elastomeric bearings for seismic isolation of building and structures. In practical situations, rubber bearings are subjected to a permanent vertical load which may change at the occurrence of the earthquake, and concurrent shear deformation, due to either service movements of the structure or earthquake-induced ground motion. The study presents an experimental procedure for the assessment of HDR specimens under combined compression and shear, reproducing the same typical load regimes which rubber isolators experience in service. Five commercial HDRs were tested according to the procedure. The results point to the importance of considering the influence of the compression stress for a correct understanding of the behavior of HDRs under cyclic shear.