A transient de photocurrent technique was used to measure the dipole moments of exciplexes formed between the electronically excited electron accepters 9,10-dicyanoanthracene (DCA) or 2,6,9,l0-tetracyanoanthracene (TCA) and methyl-substituted benzene (SB) donors. For either acceptor in benzene solution, exciplex dipole moments increase with decreasing donor oxidation potential until a maximum dipole moment of ca. 11 D is reached. A similar trend has been previously observed using other techniques, but the maximum dipole moments that we report are substantially less than is usually assumed for such systems. Mutual ion polarization is the likely cause of this difference, and a simple equation for estimating its effects is provided.