The enthalpies of dilution of Ph4PCl, Ph4AsCl, NaPh4B and R4NBr (where R is ethyl, n-propyl, n-butyl and n-pentyl) have been determined by flow microcalorimetry at 298.15 K in water. From the experimental data, the relative apparent molar enthalpies phi(L) were calculated with the aid of an extended Debye-Huckel equation. A comparison with literature values for some R4NBr was made. Ph4PCl and Ph4AsCl show similar behavior, unlike that of NaPh4B, which may be a consequence of the effect of the Na+ ion in relation to the Cl- ion.