The enthalpies of formation of (Ru) hcp solid solution and Mo5Ru3 (a phase) in the Mo-Ru system and ternary extension in the Mo-Ru-Si system at Mo56Ru37Si7 composition, have been determined by high-temperature direct reaction synthesis calorimetry at 1760K. The following values are reported: Delta H-f(1760K)(Ru)= -10.6 +/- 0.5 kJ/motat.%: Delta(H1760K)(f)(Mo5Ru3)= -7.4 +/- 0.4 kJ/mol at.%; Delta(H1760K)(f)(Mo56Ru37Si7)= -13.1 +/- 3.3 kJ/mol at.%. The results are compared with the previous values derived from e.m.f. measurements. They are also compared with the predicted values obtained by Calphad, by ab initio method combined to Calphad modelling, and derived from a thermodynamic database named "TM16.TDB". (C) 2009 Elsevier B.V. All rights reserved.