The purpose of this study was to evaluate the changes of total tumor pressure and mechanical properties as a function of increasing stress. MR elastography and perfusion measurements (FAIR method) were performed in mice with tumors xenografted subcutaneously. Tumor pressure was measured with a catheter-transducer system. Measurements were performed at different stress levels by externally compressing the tumor with an inflatable balloon. The results show that increasing the externally applied compression results in increased mechanical properties and tumor pressure and decreased perfusion. These results suggest that elevated tumor pressure can be explained by solid stress rather than fluid pressure.