Dielectrophoresis (DEP) is increasingly being explored as a means to manipulate or separate colloidal particles. The direction and strength of the DEP force depend strongly on the induced dipole strength, K, of a polarized particle, and predictions of DEP forces require carefully computed values for K. In this paper, we present the Calculation of the dipole strength using the full electrokinetic theory of Mangelsdorf and White for both static and oscillating electric fields. The effects of particle zeta potential, radius, Debye length and electrolyte composition on the magnitude and sign of Re(K) are discussed. The full theory model is compared with the extended Maxwell-Wagner (EMW) model and the results show that the EMW model can fail to predict the full Re(K) variation with frequency, even predicting Re(K) with the incorrect sign depending on system parameters. A program for the dipole strength calculation shown in this paper is available from the authors. (c) 2004 Elsevier Inc. All rights reserved.