Using an on-line solution-reaction isoperibol calorimeter, the standard molar enthalpies of reaction for the general thermochemical reaction: LnCl(3).6H(2)O(s) + 2C(9)H(7)NO(s) + CH3COONa(s) = Ln(C9H6NO)(2)(C2H3O2)(s) + NaCl(s) + 2HCl(g) + 6H(2)O(l) (Ln: Nd, Sm), were determined at T = 298.15 K, as -(56.9 +/- 1.4) and - (67.9 +/- 1.5) kJ mol(-1), respectively. From the mentioned standard molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of Ln(C9H6NO)(2)(C2H3O2)(s) (Ln: Nd, Sm), at T = 298.15 K, have been derived to be: -(1494.7 +/- 3.3) and -(1501.5 +/- 3.4) kJ mol(-1), respectively. (C) 2003 Elsevier B.V. All rights reserved.