The standard molar enthalpies of dissolution of {ZnSO(4)(.)7H(2)O(S)+Val(s)}, {ZnSO(4)(.)7H(2)O(S)+Met(s)}, Zn(Val)(SO4H2O)-H-.(s) and Zn(Met)SO4-H2O(S) (where Val is L-alpha-valine and Met is L-alpha-methionine) in 2 mol dm(-3) HCl at T = 298.15 +/- 0.001 K have been measured to be Delta(d)H(m,l)degrees = 94.588 +/- 0.025 kJ mol(-1), Delta(d)H(m,3)degrees = -46.118 +/- 0.055 kJ mol(-1), Delta(d)H(m,4)degrees = -70.619 +/- 0.051 kJ mol(-1), Delta(d)H(m,5)degrees = 58.415 +/- 0.046 kJ mol(-1), respectively. The derived molar enthalpies of formation of the complexes Zn(Val)(SO4H2O)-H-.(s) and Zn(Met)(SO4H2O)-H-.(s) are Delta(f)H(m)degrees[Zn(Val)(SO4H2O)-H-., s] = -1851 +/- 2 kJ mol(-1) and Delta(f)H(m)degrees[Zn(Met)SO4 (.) H2O, s] = -2069 +/- 0.7 J mol(-1). (c) 2005 Elsevier B.V. All rights reserved.