The (Bi + Ni) system has two intermetallic compounds, Bi0.75Ni0.25 and Bi0.5Ni0.5, which melt peritectically, at temperatures 744 K and 927 K, respectively. The enthalpies of formation of these two compounds were measured by solution calorimetric method, successive precipitation method and were calculated from experimentally determined enthalpies of peritectic decomposition. For the solution calorimetric method, liquid 'Bi' was used as solvent and the enthalpy of solution of 'Ni' and intermetallic compounds in liquid 'Bi' bath was measured. Enthalpies of formation of Bi0.75Ni0.25 and Bi0.5Ni0.5 by solution calorimetry were -2 kJ.mol(-1) and -3.7 kJ.mol(-1), respectively, at T = 298.15 K. Enthalpies of mixing of liquid alloys, measured at different temperatures, were fit into a sub-regular solution model. Different theoretical models were used to calculate thermodynamic parameters of this system. (C) 2012 Elsevier Ltd. All rights reserved.