A solubility equilibrium program GEOPROF was applied to the determination of the bubble-point depth, pressure and temperature, as well as the partial pressure profiles of the gases CO2, CH4 and N-2 between the bubble-point depth and the wellhead, in two high enthalpy geothermal wells, NSZ-2 and FAB-4 in southern Hungary. The pH, alkalinity, total carbonates, and equilibrium solubility for CaCO3, CaSO4, BaSO4, and SrSO4 along the well depth profile in the Na-K-Mg-Ca-H-Ba-Sr-Cl-Br-SO4-OH-HCO3-CO3-CO2-H2O system were also determined and the concentrations of Ca2+, Ba2+, Sr2+, H+, OH-, HCO3-, CO32-, and H2CO3* were computed at the actual temperature and CO2 pressure using the Davies and Pitzer activity calculation methods. The calculated amounts of CaCO3 scaling along the wells and at the surface were used in estimating service life. The results for well FAB-4 contain high uncertainties because of the estimated gas separation analysis data. (C) 2003 CNR. Published by Elsevier Ltd. All rights reserved.