Protonation enthalpies of ethylenediamine, 1,6-hexanediamine, 1,8-octanediamine and 1,10-decanediamine were determined at 25 degreesC in NaCl aqueous solutions, 0 < I 3 mol dm(-3) (0 < I 5 mol dm(-3), for 1,6-hexanediamine). The dependence on ionic strength of DeltaH(0) can be expressed by the equation -DeltaH(0) = -DeltaH(0) (I = 0) + a(1)I + a(2)I(2). Values of enthalpy changes at different ionic strengths made it possible to determine the temperature gradients of the specific interaction parameters of Pitzer equations. The functions DeltaG(0) and DeltaH(0) versus ionic strength are very similar and the resulting T DeltaS (0)values are quite low and fairly constant. Other empirical relationships for the dependence of both DeltaH(0) and DeltaG(0) on alkyl chain length and ionic strength are reported.