Enthalpies of mixing in water of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone (DMPU) with several alkali-metal halides (LiCl, NaCl, KCI, CsCl, KF, KBr, KI) and tetra-n-alkylammonium bromides, R4NBr (R=Me, Et, Pr, Bu) have been determined by flow microcalorimetry at 298.15 K. The results were used to calculate enthalpic pair interaction coefficients, h(NE), Of virial expansion of excess enthalpy. A decrease of the h(NE) coefficient with anionic size in the potassium halides series is observed. In the tetra-n-alkylammonium bromides series, the coefficients are positive and they become more positive when the number of carbon atoms in the hydrocarbon chain is increased. A comparison to other systems obtained from the literature is reported.