The enthalpies of dilution of aqueous solutions of {Co(en)(3)}Cl-3 and {Co(tn)(3)}Cl-3 (where en = 1,2-diaminoethane and m = 1,3-diaminopropane) have been measured up to in = 1 mol (.) kg(-1) at T = 278.15 K and atmospheric pressure with an isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies L-phi,L-m have been extracted from an empirical polynomial of the molality square root. Previously reported data at T = 298.15 K are compared with the new experimental dilution results. A noticeable decrease in L-phi,L-m was observed at every experimental concentration when temperature diminished from 298.15 K to 278.15 K. An inversion in the relative layout for the L-phi,L-m curves of aqueous {Co(en)(3)}Cl-3 and {Co(tn)(3)}Cl-3 was also found.