Describing the dissolution of H2S in aqueous electrolyte solutions under high pressures and at moderately elevated temperatures is of great interest in connection with geological storage of acid gases in deep saline aquifers. The dissolution in NaCl(aq) and CaCl2(aq) was studied by direct calorimetric measurements of the heat of mixing Delta H-mix at conditions where hydrogen sulfide is gaseous, liquid, or supercritical. The measurements were carried out using a customized mixing unit developed for an isothermal differential heat flux calorimeter Setaram BT 2.15D. The experimental technique was specifically adapted for operating with H2S taking into consideration its high toxicity. The heats of mixing were measured with the 1, 3, and 5 mol.kg(-1) NaCl(aq) at target temperatures of 323, 353, and 393 K and at pressures up to 13, 31, and 20 MPa, respectively. Analogous measurements were performed with 0.33 and 1 mol.kg(-1) CaCl2(aq) at the medium temperature and pressures up to 31 MPa. The experiments were always carried out in the regions where the solution is unsaturated and saturated by H2S. The obtained concentration dependence of Delta H-mix allowed one to derive simultaneously both the limiting enthalpy of solution Delta H-sol of H2S and the concentration of its solubility limit. Comparison with the earlier published data for H2S in pure water at identical conditions (Koschel et al. Ind. Eng. Chem. Res. 2007, 46, 1421-1430) gives the information on the salting-out effect and its dependence on temperature and pressure, as well as on the concentration and nature of the salt. The newly obtained data are also compared with those resulting from the measurements with supercritical CO2 at analogous conditions (Koschel et al. Fluid Phase Equilib. 2006, 247, 107-120).