Vapor pressure measurements, in terms of a (non-)isothermal isopiestic method, were carried out in the system Cd-Pr between 749 K and 1067 K (476°C and 794°C). Thermodynamic activities of cadmium as a function of temperature were obtained directly for the composition ranging from 50.0 to 85.7 at. pct Cd. From these results, partial molar enthalpies of mixing of Cd were derived for the corresponding composition range. The activity values of Cd were converted to an average sample temperature of 823 K (550°C) by applying an integrated form of the Gibbs-Helmholtz equation. These data indicate that Cd 2 Pr and Cd 58 Pr 13 are probably the most stable intermetallic compounds in this system. Using an activity value of Pr from the literature as integration constant, Gibbs-Duhem integration was performed, and integral Gibbs energies are presented at 823 K (550°C), referred to Cd(l) and a-Pr(s). Gibbs energies of formation at the stoichiometric compositions of the phases Cd 6 Pr, Cd 58 Pr 13 , Cd 45 Pr 11 , Cd 3 Pr, and Cd 2 Pr were determined to be about À18.8, À23.5, À24.8, À28.7, and À33.8 kJ g-atom À1 at 823 K (550°C), respectively.