Steady-state microelectrode voltammetry has been used to obtain reversible half-wave potentials for the two reduction waves of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the oxidation wave of ferrocene in acetonitrile with concentrations of tetramethylammonium hexafluorophosphate electrolyte ranging from 1 to 70 mM. The dependence of the first half-wave potential of TCNQ, referred to the half-wave potential of ferrocene, on ionic strength was adequately accounted for by changes in activity coefficients of ferrocenium ions and TCNQ radical anions as predicted by the Debye-Huckel equation. Extrapolation to zero ionic strength gives -0.233 V for the infinite-dilution half-wave potential of TCNQ vs ferrocene. Application of a small correction for unequal diffusion coefficients yields -0.226 V for the standard potential of TCNQ vs ferrocene. It is concluded that there is no significant ion pairing of either ferrocenium ions with hexafluorophosphate from the electrolyte or TCNQ radical anions with tetramethylammonium ions of the electrolyte. Similarly, plots of the difference between the two half-wave potentials of TCNQ vs the square root of ionic strength can be accounted for by activity coefficients as predicted by theory. Extrapolation to infinite dilution and application of the correction for unequal diffusion coefficients gives 0.585 V for the difference between the standard potentials of TCNQ. Ion pairing between tetramethylammonium ions and TCNQ dianions is also negligible. Also, no ion pairing is detected with 10 mM CsClO4, 5 mM RbClO4, or 5 mM KClO4 However, in agreement with earlier studies, results for 10 mM LiClO4 were consistent with extensive one-to-one ion pairing between lithium ions and dianions of TCNQ.