At the Gesellschaft für Schwerionenforschung (GSI, Darmstadt) intense beams of energetic heavy ions have been used to generate high-energy-density (HED) state in matter by impact on solid targets. Recently, we have developed a new method by which we use the same heavy ion beam that heats the target to provide information about the physical state of the interior of the target (Varentsov et al., 2001). This is accomplished by measuring the energy loss dynamics (ELD) of the beam emerging from the back surface of the target. For this purpose, a new time-resolving energy loss spectrometer (scintillating Bragg-peak (SBP) spectrometer) has been developed. In our experiments we have measured energy loss dynamics of intense beams of 238U, 86Kr, 40Ar, and 18O ions during the interaction with solid rare-gas targets, such as solid Ne and solid Xe. We observed continuous reduction in the energy loss during the interaction time due to rapid hydrodynamic response of the ion-beam-heated target matter. These are the first measurements of this kind. Two-dimensional hydrodynamic simulations were carried out using the beam and target parameters of the experiments. The conducted research has established that the ELD measurement technique is an excellent diagnostic method for HED matter. It specifically allows for direct and quantitative comparison with the results of hydrodynamic simulations, providing experimental data for verification of computer codes and underlying theoretical models. The ELD measurements will be used as a standard diagnostics in the future experiments on investigation of the HED matter induced by intense heavy ion beams, such as the HI-HEX (Heavy Ion Heating and EXpansion) EOS studies (Hoffmann et al., 2002).