Ni(P) is used in electronics as a protective layer during the soldering process. New thermodynamic information on Ni-P alloys has been obtained in the Ni-rich part (up to the molar fraction x(p) = 0.40) by using a high-temperature direct drop calorimeter. The experimental trend of Delta(f)H degrees [kJ.(mol of atoms)(-1)] of the Ni-P alloys versus composition (x(p)) has been plotted and the following standard enthalpy of formation [Delta(f)H degrees +/- 2 kJ.(mol of atoms)(-1)] values interpolated for the Ni-rich phases: 48.0 (Ni(3)P), -55.0 (Ni(5)P(2)), -56.0 (Ni(12)P(5)), and -61.0 (NiP(2)). Our results have been compared with those reported in the literature and discussed.