We report on data for the concentration dependence of the static dielectric constant epsilon (S) of solutions of tetra-n-butylammonium naphtylsulfonate (TBNAS) in toluene derived from measurements of the frequency-dependent complex permittivity. The system shows an upper consolute point at T-c = 329 K and a mole fraction X-c = 0.0235 of the salt. The measurements were performed along a slightly supercritical isotherm at 338.15 K at mole fractions 0.01 less than or equal toX less than or equal to0.068. epsilon (S) increases with increasing salt concentration. At the critical point epsilon (S)=(3.1 +/-0.05) compared with epsilon (S)=2.35 for pure toluene. In the concentration range covered by the experiments, the effective dipole moments calculated from these data are of the order of mu (eff)=5 D, which is distinctly lower than an estimate for the isolated molecule, mu (0)congruent to 18 D. The difference is attributed to compensation effects due to preferred antiparallel ion pair orientations, as described by a Kirkwood-Frohlich-type theory with correlation factors of g(K)<1. At the critical point we find g(K)congruent to0.05. Due to these orientational correlations, dipole-dipole interactions between ion pairs may provide a significantly smaller contribution to the free energy than predicted by theory. This may explain the good performance of theories that ignore dipole-dipole interactions between pairs. (C) 2001 American Institute of Physics.