The standard enthalpies of formation of NaMgH3 and NaMgH2F were determined by calorimetry using their reaction with hydrochloric acid aqueous solution (0.5 M HCl): Delta(f)H(0) (NaMgH3, cr, 298 K) = -(231 +/- 4) kJ mol(-1) Delta(f)H(0)(NaMgH2F, cr, 298 K) = -(720 +/- 8) kJ mol(-1) The standard enthalpy of formation of NaMgF2H was estimated on the basis of the experimental measurements and on the value of sodium-magnesium fluoride (NaMgF3) noted in the literature: Delta(f)H(0)(NaMgF2H, cr, 298 K) = -(1221 +/- 7) kJ mol(-1).