Excess enthalpies in water of dimethyl sulfoxide (DMSO) with various electrolytes (CsI, Me4NBr, Et4NBr, Pr4NBr, Bu4NBr and Pen(4)NBr) have been determined by flow microcalorimetry at 298.15 K. Enthalpic pair interaction coefficients, h(NE). Of the virial expansion of the mixing enthalpy were calculated. The interaction of DMSO with CsI, Me4NBr, Et4NBr gives negative and that with the remaining electrolytes gives positive coefficients. In the tetraalkylammonium series, h(NE) becomes increasingly positive when the number of carbon atoms in the hydrocarbon chain is increased.