The standard Gibbs free energy of formation of the intermetallic compound Ni3Al and the aluminium activity have been determined in the temperature range (820 to 920) K with the help of solid-state galvanic cells involving calcium fluoride as an electrolyte. The behaviour of the molar Gibbs free energy of mixing for Ni3Al at 900 K plotted as a function of the mole fraction of Ni, along with those determined previously for other intermetallic compounds in the Ni-Al system, indicates consistency of all the data obtained. (C) 2004 Elsevier Ltd. All rights reserved.